rfc8706xml2.original.xml   rfc8706.xml 
<?xml version="1.0" encoding="US-ASCII"?> <?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd">
<?rfc toc="yes"?> <!DOCTYPE rfc SYSTEM "rfc2629-xhtml.ent">
<?rfc tocompact="yes"?>
<?rfc tocdepth="3"?> <rfc number="8706" xmlns:xi="http://www.w3.org/2001/XInclude" category="std"
<?rfc tocindent="yes"?> consensus="true" docName="draft-ietf-lsr-isis-rfc5306bis-09" ipr="trust2009
<?rfc symrefs="yes"?> 02"
<?rfc sortrefs="yes"?> obsoletes="5306" updates="" submissionType="IETF" xml:lang="en"
<?rfc comments="yes"?> tocInclude="true" symRefs="true" sortRefs="true" version="3">
<?rfc inline="yes"?>
<?rfc compact="yes"?>
<?rfc subcompact="no"?>
<rfc category="std" docName="draft-ietf-lsr-isis-rfc5306bis-09"
ipr="trust200902" obsoletes="5306">
<front>
<title abbrev="restart-signalling-for-IS-IS">Restart Signaling for
IS-IS</title>
<!-- xml2rfc v2v3 conversion 2.33.0 -->
<front>
<title>Restart Signaling for IS-IS</title>
<seriesInfo name="RFC" value="8706" />
<author fullname="Les Ginsberg" initials="L." surname="Ginsberg"> <author fullname="Les Ginsberg" initials="L." surname="Ginsberg">
<organization>Cisco Systems, Inc.</organization> <organization>Cisco Systems, Inc.</organization>
<address> <address>
<postal> <postal>
<street/> <street/>
<city/> <city/>
<code/> <code/>
<country/> <country/>
</postal> </postal>
<email>ginsberg@cisco.com</email> <email>ginsberg@cisco.com</email>
</address> </address>
</author> </author>
<author fullname="Paul Wells" initials="P." surname="Wells"> <author fullname="Paul Wells" initials="P." surname="Wells">
<organization>Cisco Systems, Inc.</organization> <organization>Cisco Systems, Inc.</organization>
<address> <address>
<postal> <postal>
<street/> <street/>
<city/> <city/>
<region/> <region/>
<code/> <code/>
<country/> <country/>
</postal> </postal>
<email>pauwells@cisco.com</email> <email>pauwells@cisco.com</email>
</address> </address>
</author> </author>
<date month="February" year="2020"/>
<date day="19" month="September" year="2019"/>
<area>Routing</area> <area>Routing</area>
<workgroup>IS-IS for IP Internets</workgroup> <workgroup>IS-IS for IP Internets</workgroup>
<keyword>IGP</keyword> <keyword>IGP</keyword>
<keyword>IS-IS</keyword> <keyword>IS-IS</keyword>
<keyword>graceful restart</keyword> <keyword>graceful restart</keyword>
<abstract> <abstract>
<t>This document describes a mechanism for a restarting router to signal <t>This document describes a mechanism for a restarting router to signal
to its neighbors that it is restarting, allowing them to reestablish to its neighbors that it is restarting, allowing them to reestablish
their adjacencies without cycling through the down state, while still their adjacencies without cycling through the DOWN state while still
correctly initiating database synchronization.</t> correctly initiating database synchronization.</t>
<t>This document additionally describes a mechanism for a router to <t>This document additionally describes a mechanism for a router to
signal its neighbors that it is preparing to initiate a restart while signal its neighbors that it is preparing to initiate a restart while
maintaining forwarding plane state. This allows the neighbors to maintaining forwarding-plane state. This allows the neighbors to
maintain their adjacencies until the router has restarted, but also maintain their adjacencies until the router has restarted but also
allows the neighbors to bring the adjacencies down in the event of other allows the neighbors
to bring the adjacencies down in the event of other
topology changes.</t> topology changes.</t>
<t>This document additionally describes a mechanism for a restarting <t>This document additionally describes a mechanism for a restarting
router to determine when it has achieved Link State Protocol Data Unit router to determine when it has achieved Link State Protocol Data Unit
(LSP) database synchronization with its neighbors and a mechanism to (LSP) database synchronization with its neighbors and a mechanism to
optimize LSP database synchronization, while minimizing transient optimize LSP database synchronization while minimizing transient
routing disruption when a router starts.</t> routing disruption when a router starts.</t>
<t>This document obsoletes RFC 5306.</t> <t>This document obsoletes RFC 5306.</t>
</abstract> </abstract>
<note title="Requirements Language">
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP 14
<xref target="RFC2119"/> <xref target="RFC8174"/> when, and only when,
they appear in all capitals, as shown here.</t>
</note>
</front> </front>
<middle> <middle>
<section title="Overview"> <section numbered="true" toc="default">
<name>Overview</name>
<t>The Intermediate System to Intermediate System (IS-IS) routing <t>The Intermediate System to Intermediate System (IS-IS) routing
protocol [RFC1195] [ISO10589] is a link state intra-domain routing protocol <xref target="RFC1195" format="default"/> <xref
target="ISO10589" format="default"/> is a link state intra-domain routing
protocol. Normally, when an IS-IS router is restarted, temporary protocol. Normally, when an IS-IS router is restarted, temporary
disruption of routing occurs due to events in both the restarting router disruption of routing occurs due to events in both the restarting router
and the neighbors of the restarting router.</t> and the neighbors of the restarting router.</t>
<t>The router that has been restarted computes its own routes before <t>The router that has been restarted computes its own routes before
achieving database synchronization with its neighbors. The results of achieving database synchronization with its neighbors. The results of
this computation are likely to be non-convergent with the routes this computation are likely to be non-convergent with the routes
computed by other routers in the area/domain.</t> computed by other routers in the area/domain.</t>
<t>Neighbors of the restarting router detect the restart event and cycle <t>Neighbors of the restarting router detect the restart event and cycle
their adjacencies with the restarting router through the down state. The their adjacencies with the restarting router through the DOWN state. The
cycling of the adjacency state causes the neighbors to regenerate their cycling of the adjacency state causes the neighbors to regenerate their
LSPs describing the adjacency concerned. This in turn causes a temporary LSPs describing the adjacency concerned. This in turn causes a temporary
disruption of routes passing through the restarting router.</t> disruption of routes passing through the restarting router.</t>
<t>In certain scenarios, the temporary disruption of the routes is <t>In certain scenarios, the temporary disruption of the routes is
highly undesirable. This document describes mechanisms to avoid or highly undesirable. This document describes mechanisms to avoid or
minimize the disruption due to both of these causes.</t> minimize the disruption due to both of these causes.</t>
<t>When an adjacency is reinitialized as a result of a neighbor <t>When an adjacency is reinitialized as a result of a neighbor
restarting, a router does three things:</t> restarting, a router does three things:</t>
<ol spacing="normal" type="1">
<t><list style="numbers"> <li>It causes its own LSP(s) to be regenerated, thus triggering
<t>It causes its own LSP(s) to be regenerated, thus triggering SPF Shortest Path First (SPF)
runs throughout the area (or in the case of Level 2, throughout the runs throughout the area (or in the case of Level 2, throughout the
domain).</t> domain).</li>
<li>It sets SRMflags on its own LSP database on the adjacency
<t>It sets SRMflags on its own LSP database on the adjacency concerned.</li>
concerned.</t> <li>In the case of a Point-to-Point link, it transmits a complete set
of Complete Sequence Number PDUs (CSNPs), over the adjacency.</li>
<t>In the case of a Point-to-Point link, it transmits a complete set </ol>
of Complete Sequence Number PDUs (CSNPs), over the adjacency.</t>
</list></t>
<t>In the case of a restarting router process, the first of these is <t>In the case of a restarting router process, the first of these is
highly undesirable, but the second is essential in order to ensure highly undesirable, but the second is essential in order to ensure
synchronization of the LSP database.</t> synchronization of the LSP database.</t>
<t>The third action above minimizes the number of LSPs that must be <t>The third action above minimizes the number of LSPs that must be
exchanged and, if made reliable, provides a means of determining when exchanged and, if made reliable, provides a means of determining when
the LSP databases of the neighboring routers have been synchronized. the LSP databases of the neighboring routers have been synchronized.
This is desirable whether or not the router is being restarted (so that This is desirable whether or not the router is being restarted (so that
the overload bit can be cleared in the router's own LSP, for the overload bit can be cleared in the router's own LSP, for
example).</t> example).</t>
<t>This document describes a mechanism for a restarting router to signal <t>This document describes a mechanism for a restarting router to signal
to its neighbors that it is restarting. The mechanism further allows the to its neighbors that it is restarting. The mechanism further allows the
neighbors to reestablish their adjacencies with the restarting router neighbors to reestablish their adjacencies with the restarting router
without cycling through the down state, while still correctly initiating without cycling through the DOWN state while still correctly initiating
database synchronization.</t> database synchronization.</t>
<t>This document additionally describes a mechanism for a restarting <t>This document additionally describes a mechanism for a restarting
router to determine when it has achieved LSP database synchronization router to determine when it has achieved LSP database synchronization
with its neighbors and a mechanism to optimize LSP database with its neighbors and a mechanism to optimize LSP database
synchronization and minimize transient routing disruption when a router synchronization and minimize transient routing disruption when a router
starts.</t> starts.</t>
<t>It is assumed that the three-way handshake <xref target="RFC5303" forma
<t>It is assumed that the three-way handshake <xref target="RFC5303"/> t="default"/>
is being used on Point-to-Point circuits.</t> is being used on Point-to-Point circuits.</t>
</section> </section>
<section numbered="true" toc="default" anchor="conventions">
<section title="Conventions Used in This Document"> <name>Conventions Used in This Document</name>
<t>If the control and forwarding functions in a router can be maintained <t>If the control and forwarding functions in a router can be maintained
independently, it is possible for the forwarding function state to be independently, it is possible for the forwarding function state to be
maintained across a resumption of control function operations. This maintained across a resumption of control function operations. This
functionality is assumed when the terms "restart/restarting" are used in functionality is assumed when the terms "restart/restarting" are used in
this document.</t> this document.</t>
<t>The terms "start/starting" are used to refer to a router in which the <t>The terms "start/starting" are used to refer to a router in which the
control function has either commenced operations for the first time or control function has either commenced operations for the first time or
has resumed operations, but the forwarding functions have not been has resumed operations, but the forwarding functions have not been
maintained in a prior state.</t> maintained in a prior state.</t>
<t>The terms "(re)start/(re)starting" are used when the text is <t>The terms "(re)start/(re)starting" are used when the text is
applicable to both a "starting" and a "restarting" router.</t> applicable to both a "starting" and a "restarting" router.</t>
<t>The terms "normal IIH" or "IIH normal" refer to IS-IS Hellos (IIHs) <t>The terms "normal IIH" or "IIH normal" refer to IS-IS Hellos (IIHs)
in which the Restart TLV (defined later in this document) has no flags in which the Restart TLV (defined later in this document) has no flags
set.</t> set.</t>
<section numbered="true" toc="default">
<name>Requirements Language</name>
<t>
The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp14>REQU
IRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL
NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14>
RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
"<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this document are to
be interpreted as
described in BCP&nbsp;14 <xref target="RFC2119"/> <xref target="RFC8174"/>
when, and only when, they appear in all capitals, as shown here.
</t>
</section>
</section> </section>
<section numbered="true" toc="default">
<section title="Approach"> <name>Approach</name>
<section title="Timers"> <section numbered="true" toc="default">
<t>Three additional timers, T1, T2, and T3, are required to support <name>Timers</name>
<t>Three additional timers (T1, T2, and T3) are required to support
the mechanisms defined in this document. Timers T1 and T2 are used the mechanisms defined in this document. Timers T1 and T2 are used
both by a restarting router and a starting router. Timer T3 is used both by a restarting router and a starting router. Timer T3 is used
only by a restarting router.</t> only by a restarting router.</t>
<t>NOTE: These timers are NOT applicable to a router that is
<t>NOTE: These timers are NOT applicable to a router which is
preparing to do a planned restart.</t> preparing to do a planned restart.</t>
<t>An instance of the timer T1 is maintained per interface and
<t>An instance of the timer T1 is maintained per interface, and
indicates the time after which an unacknowledged (re)start attempt indicates the time after which an unacknowledged (re)start attempt
will be repeated. A typical value is 3 seconds.</t> will be repeated. A typical value is 3 seconds.</t>
<t>An instance of the timer T2 is maintained for each LSP database <t>An instance of the timer T2 is maintained for each LSP database
(LSPDB) present in the system. For example, for a Level 1/2 system, (LSPDB) present in the system. For example, for a Level 1/2 system,
there will be an instance of the timer T2 for Level 1 and an instance there will be an instance of the timer T2 for Level 1 and an instance
for Level 2. This is the maximum time that the system will wait for for Level 2. This is the maximum time that the system will wait for
LSPDB synchronization. A typical value is 60 seconds.</t> LSPDB synchronization. A typical value is 60 seconds.</t>
<t>A single instance of the timer T3 is maintained for the entire <t>A single instance of the timer T3 is maintained for the entire
system. It indicates the time after which the router will declare that system. It indicates the time after which the router will declare that
it has failed to achieve database synchronization (by setting the it has failed to achieve database synchronization (by setting the
overload bit in its own LSP). This is initialized to 65535 seconds, overload bit in its own LSP). This is initialized to 65535 seconds
but is set to the minimum of the remaining times of received IIHs but is set to the minimum of the remaining times of received IIHs
containing a restart TLV with the Restart Acknowledgement (RA) set and containing a Restart TLV with the Restart Acknowledgement (RA) set and
an indication that the neighbor has an adjacency in the "UP" state to an indication that the neighbor has an adjacency in the UP state to
the restarting router. (See Section 3.2.1a.)</t> the restarting router. (See <xref target="itema" format="none">item a</x
ref> in <xref target="useofrrrabitssection"/>.)</t>
</section> </section>
<section numbered="true" toc="default">
<section title="Restart TLV"> <name>Restart TLV</name>
<t>A new TLV is defined to be included in IIH PDUs. The TLV includes <t>A new TLV is defined to be included in IIH PDUs. The TLV includes
flags that are used to convey information during a (re)start. The flags that are used to convey information during a (re)start. The
absence of this TLV indicates that the sender supports none of the absence of this TLV indicates that the sender supports none of the
functionality defined in this document. Therefore, if a router functionality defined in this document. Therefore, if a router
supports any of the functionality defined in this document it MUST supports any of the functionality defined in this document it <bcp14>MUS
include this TLV in all transmitted IIHs.</t> T</bcp14> include this TLV in all transmitted IIHs.</t>
<figure> <dl newline="true" spacing="normal">
<artwork><![CDATA[ Type 211
Length: Number of octets in the Value field (1 to (3 + ID Length)) <dt>Type:</dt><dd>211</dd>
Value <dt>Length:</dt><dd>Number of octets in the Value field (1 to (3 + ID
Length))</dd>
No. of octets <dt>Value:</dt><dd>
<artwork><![CDATA[
No. of octets
+-----------------------+ +-----------------------+
| Flags | 1 | Flags | 1
+-----------------------+ +-----------------------+
| Remaining Time | 2 | Remaining Time | 2
+-----------------------+ +-----------------------+
| Restarting Neighbor ID| ID Length | Restarting Neighbor ID| ID Length
+-----------------------+ +-----------------------+
]]></artwork>
Flags (1 octet) <dl newline="true" spacing="normal">
0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+
|Reserved|PA|PR|SA|RA|RR|
+--+--+--+--+--+--+--+--+
RR - Restart Request <dt>Flags (1 octet)</dt>
RA - Restart Acknowledgement <dd>
SA - Suppress adjacency advertisement <artwork><![CDATA[
PR - Restart is planned 0 1 2 3 4 5 6 7
PA - Planned restart acknowledgement +--+--+--+--+--+--+--+--+
|Reserved|PA|PR|SA|RA|RR|
+--+--+--+--+--+--+--+--+
]]></artwork>
Remaining Time (2 octets) <dl newline="false" spacing="compact">
<dt>RR -</dt><dd>Restart Request</dd>
<dt>RA -</dt><dd>Restart Acknowledgement</dd>
<dt>SA -</dt><dd>Suppress adjacency advertisement</dd>
<dt>PR -</dt><dd>Restart is planned</dd>
<dt>PA -</dt><dd>Planned restart acknowledgement</dd>
</dl>
</dd>
Remaining holding time (in seconds). <dt>Remaining Time (2 octets)</dt>
<dd><t>Remaining Holding Time (in seconds).</t>
Required when the RA, PR, or PA bit is set. Otherwise <t>Required when the RA, PR, or PA bit is set. Otherwise, this field
this field SHOULD be omitted when sent and <bcp14>SHOULD</bcp14> be omitted when sent and <bcp14>MUST</bcp14> be ignored
MUST be ignored when received. when received.</t>
</dd>
Restarting Neighbor System ID (ID Length octets) <dt>Restarting Neighbor System ID (ID Length octets)</dt>
The System ID of the neighbor to which an RA/PA refers. <dd>
<t>The System ID of the neighbor to which an RA/PA refers.</t>
Required when the RA or PA bit is set. Otherwise <t>Required when the RA or PA bit is set. Otherwise,
this field SHOULD be omitted when sent and this field <bcp14>SHOULD</bcp14> be omitted when sent and
MUST be ignored when received. <bcp14>MUST</bcp14> be ignored when received.</t>
Note: Very early draft versions of the restart functionality <t>Note: Very early draft versions of the restart functionality
did not include the Restarting Neighbor System ID in the TLV. did not include the Restarting Neighbor System ID in the TLV.
RFC 5306 allowed for the possibility of interoperating with RFC 5306 allowed for the possibility of interoperating with
legacy implementations by stating that a router that legacy implementations by stating that a router that
is expecting an RA on a LAN circuit should assume that the is expecting an RA on a LAN circuit should assume that the
acknowledgement is directed at the local system if the TLV acknowledgement is directed at the local system if the TLV
is received with RA set and Restarting Neighbor System ID is received with RA set and Restarting Neighbor System ID
is not present. It is an implementation choice whether to is not present. It is an implementation choice whether to
continue to accept (on a LAN) a TLV with RA set and continue to accept (on a LAN) a TLV with RA set and
Restarting Neighbor System ID absent. Note that the omission Restarting Neighbor System ID absent. Note that the omission
of the Restarting Neighbor System ID only introduces ambiguity of the Restarting Neighbor System ID only introduces ambiguity
in the case where there are multiple systems on a LAN in the case where there are multiple systems on a LAN
simultaneously performing restart. simultaneously performing restart.</t>
</dd>
]]></artwork> </dl>
</figure> </dd>
</dl>
<t>The RR and SA flags may both be set in the TLV under the conditions <t>The RR and SA flags may both be set in the TLV under the conditions
described in Section 3.3.2. All other combinations where multiple described in <xref target="adjacencyacqsection"/>. All other combination
flags are set are invalid and MUST NOT be transmitted. Received TLVs s where multiple
which have invalid flag combinations set MUST be ignored.</t> flags are set are invalid and <bcp14>MUST NOT</bcp14> be transmitted. Re
ceived TLVs
that have invalid flag combinations set <bcp14>MUST</bcp14> be ignored.<
/t>
<section title="Use of RR and RA Bits"> <section numbered="true" toc="default" anchor="useofrrrabitssection">
<name>Use of RR and RA Bits</name>
<t>The RR bit is used by a (re)starting router to signal to its <t>The RR bit is used by a (re)starting router to signal to its
neighbors that a (re)start is in progress, that an existing neighbors that a (re)start is in progress, that an existing
adjacency SHOULD be maintained even under circumstances when the adjacency <bcp14>SHOULD</bcp14> be maintained even under circumstances when the
normal operation of the adjacency state machine would require the normal operation of the adjacency state machine would require the
adjacency to be reinitialized, to request a set of CSNPs, and to adjacency to be reinitialized, to request a set of CSNPs, and to
request setting of the SRMflags.</t> request setting of the SRMflags.</t>
<t>The RA bit is sent by the neighbor of a (re)starting router to <t>The RA bit is sent by the neighbor of a (re)starting router to
acknowledge the receipt of a restart TLV with the RR bit set.</t> acknowledge the receipt of a Restart TLV with the RR bit set.</t>
<t>When the neighbor of a (re)starting router receives an IIH with <t>When the neighbor of a (re)starting router receives an IIH with
the restart TLV having the RR bit set, if there exists on this the Restart TLV having the RR bit set, if there exists on this
interface an adjacency in state "UP" with the same System ID, and in interface an adjacency in the UP state with the same System ID and, in
the case of a LAN circuit, with the same source LAN address, then, the case of a LAN circuit, with the same source LAN address, then
irrespective of the other contents of the "Intermediate System irrespective of the other contents of the "Intermediate System
Neighbors" option (LAN circuits) or the "Point-to-Point Three-Way Neighbors" option (LAN circuits) or the "Point-to-Point Three-Way
Adjacency" option (Point-to-Point circuits):</t> Adjacency" option (Point-to-Point circuits):</t>
<ol spacing="normal" type="a">
<t><list style="letters"> <li anchor="itema">the state of the adjacency is not changed. If thi
<t>the state of the adjacency is not changed. If this is the s is the
first IIH with the RR bit set that this system has received first IIH with the RR bit set that this system has received
associated with this adjacency, then the adjacency is marked as associated with this adjacency, then the adjacency is marked as
being in "Restart mode" and the adjacency holding time is being in "Restart mode" and the adjacency Holding Time is
refreshed -- otherwise, the holding time is not refreshed. The refreshed -- otherwise, the Holding Time is not refreshed. The
"remaining time" transmitted according to (b) below MUST reflect Remaining Time transmitted according to (b) below <bcp14>MUST</bcp
14> reflect
the actual time after which the adjacency will now expire. the actual time after which the adjacency will now expire.
Receipt of an IIH with the RR bit reset will clear the "Restart Receipt of an IIH with the RR bit reset will clear the "Restart
mode" state. This procedure allows the restarting router to mode" state. This procedure allows the restarting router to
cause the neighbor to maintain the adjacency long enough for cause the neighbor to maintain the adjacency long enough for
restart to successfully complete, while also preventing restart to successfully complete while also preventing
repetitive restarts from maintaining an adjacency indefinitely. repetitive restarts from maintaining an adjacency indefinitely.
Whether or not an adjacency is marked as being in "Restart mode" Whether or not an adjacency is marked as being in "Restart mode"
has no effect on adjacency state transitions.</t> has no effect on adjacency state transitions.</li>
<li>immediately (i.e., without waiting for any currently running
<t>immediately (i.e., without waiting for any currently running timer interval to expire but with a small random delay of a few
timer interval to expire, but with a small random delay of a few
tens of milliseconds on LANs to avoid "storms") transmit over tens of milliseconds on LANs to avoid "storms") transmit over
the corresponding interface an IIH including the restart TLV the corresponding interface an IIH including the Restart TLV
with the RR bit clear and the RA bit set, in the case of with the RR bit clear and the RA bit set, in the case of
Point-to-Point adjacencies having updated the "Point-to-Point Point-to-Point adjacencies having updated the "Point-to-Point
Three-Way Adjacency" option to reflect any new values received Three-Way Adjacency" option to reflect any new values received
from the (re)starting router. (This allows a restarting router from the (re)starting router. (This allows a restarting router
to quickly acquire the correct information to place in its to quickly acquire the correct information to place in its
hellos.) The "Remaining Time" MUST be set to the current time hellos.) The Remaining Time <bcp14>MUST</bcp14> be set to the curr ent time
(in seconds) before the holding timer on this adjacency is due (in seconds) before the holding timer on this adjacency is due
to expire. If the corresponding interface is a LAN interface, to expire. If the corresponding interface is a LAN interface,
then the Restarting Neighbor System ID SHOULD be set to the then the Restarting Neighbor System ID <bcp14>SHOULD</bcp14> be se t to the
System ID of the router from which the IIH with the RR bit set System ID of the router from which the IIH with the RR bit set
was received. This is required to correctly associate the was received. This is required to correctly associate the
acknowledgement and holding time in the case where multiple acknowledgement and Holding Time in the case where multiple
systems on a LAN restart at approximately the same time. This systems on a LAN restart at approximately the same time. This
IIH SHOULD be transmitted before any LSPs or SNPs are IIH <bcp14>SHOULD</bcp14> be transmitted before any LSPs or SNPs a
transmitted as a result of the receipt of the original IIH.</t> re
transmitted as a result of the receipt of the original IIH.</li>
<t>if the corresponding interface is a Point-to-Point interface, <li anchor="itemc">if the corresponding interface is a Point-to-Poin
t interface,
or if the receiving router has the highest LnRouterPriority or if the receiving router has the highest LnRouterPriority
(with the highest source MAC (Media Access Control) address (with the highest source Media Access Control (MAC) address
breaking ties) among those routers to which the receiving router breaking ties) among those routers to which the receiving router
has an adjacency in state "UP" on this interface whose IIHs has an adjacency in the UP state on this interface whose IIHs
contain the restart TLV, excluding adjacencies to all routers contain the Restart TLV, excluding adjacencies to all routers
which are considered in "Restart mode" (note the actual DIS is that are considered in "Restart mode" (note the actual
Designated Intermediate System (DIS) is
NOT changed by this process), initiate the transmission over the NOT changed by this process), initiate the transmission over the
corresponding interface of a complete set of CSNPs, and set corresponding interface of a complete set of CSNPs, and set
SRMflags on the corresponding interface for all LSPs in the SRMflags on the corresponding interface for all LSPs in the
local LSP database.</t> local LSP database.</li>
</list>Otherwise (i.e., if there was no adjacency in the "UP" </ol>
<t>Otherwise (i.e., if there was no adjacency in the UP
state to the System ID in question), process the IIH as normal by state to the System ID in question), process the IIH as normal by
reinitializing the adjacency and setting the RA bit in the returned reinitializing the adjacency and setting the RA bit in the returned
IIH.</t> IIH.</t>
</section> </section>
<section numbered="true" toc="default" anchor="useofsabitsection">
<section title="Use of the SA Bit"> <name>Use of the SA Bit</name>
<t>The SA bit is used by a starting router to request that its <t>The SA bit is used by a starting router to request that its
neighbor suppress advertisement of the adjacency to the starting neighbor suppress advertisement of the adjacency to the starting
router in the neighbor's LSPs.</t> router in the neighbor's LSPs.</t>
<t>A router that is starting has no maintained forwarding function <t>A router that is starting has no maintained forwarding function
state. This may or may not be the first time the router has started. state. This may or may not be the first time the router has started.
If this is not the first time the router has started, copies of LSPs If this is not the first time the router has started, copies of LSPs
generated by this router in its previous incarnation may exist in generated by this router in its previous incarnation may exist in
the LSP databases of other routers in the network. These copies are the LSP databases of other routers in the network. These copies are
likely to appear "newer" than LSPs initially generated by the likely to appear "newer" than LSPs initially generated by the
starting router due to the reinitialization of LSP fragment sequence starting router due to the reinitialization of LSP fragment sequence
numbers by the starting router. This may cause temporary blackholes numbers by the starting router. This may cause temporary blackholes
to occur until the normal operation of the update process causes the to occur until the normal operation of the update process causes the
starting router to regenerate and flood copies of its own LSPs with starting router to regenerate and flood copies of its own LSPs with
skipping to change at line 382 skipping to change at line 350
likely to appear "newer" than LSPs initially generated by the likely to appear "newer" than LSPs initially generated by the
starting router due to the reinitialization of LSP fragment sequence starting router due to the reinitialization of LSP fragment sequence
numbers by the starting router. This may cause temporary blackholes numbers by the starting router. This may cause temporary blackholes
to occur until the normal operation of the update process causes the to occur until the normal operation of the update process causes the
starting router to regenerate and flood copies of its own LSPs with starting router to regenerate and flood copies of its own LSPs with
higher sequence numbers. The temporary blackholes can be avoided if higher sequence numbers. The temporary blackholes can be avoided if
the starting router's neighbors suppress advertising an adjacency to the starting router's neighbors suppress advertising an adjacency to
the starting router until the starting router has been able to the starting router until the starting router has been able to
propagate newer versions of LSPs generated by previous propagate newer versions of LSPs generated by previous
incarnations.</t> incarnations.</t>
<t>When a router receives an IIH with the Restart TLV having the SA
<t>When a router receives an IIH with the restart TLV having the SA bit set, if there exists on this interface an adjacency in the UP stat
bit set, if there exists on this interface an adjacency in state e
"UP" with the same System ID, and in the case of a LAN circuit, with with the same System ID and, in the case of a LAN circuit, with
the same source LAN address, then the router MUST suppress the same source LAN address, then the router <bcp14>MUST</bcp14> suppr
ess
advertisement of the adjacency to the neighbor in its own LSPs. advertisement of the adjacency to the neighbor in its own LSPs.
Until an IIH with the SA bit clear has been received, the neighbor Until an IIH with the SA bit clear has been received, the neighbor
advertisement MUST continue to be suppressed. If the adjacency advertisement <bcp14>MUST</bcp14> continue to be suppressed. If the ad
transitions to the "UP" state, the new adjacency MUST NOT be jacency
transitions to the UP state, the new adjacency <bcp14>MUST NOT</bcp14>
be
advertised until an IIH with the SA bit clear has been received.</t> advertised until an IIH with the SA bit clear has been received.</t>
<t>Note that a router that suppresses advertisement of an adjacency <t>Note that a router that suppresses advertisement of an adjacency
MUST NOT use this adjacency when performing its SPF calculation. In <bcp14>MUST NOT</bcp14> use this adjacency when performing its SPF cal culation. In
particular, if an implementation follows the example guidelines particular, if an implementation follows the example guidelines
presented in [ISO10589], Annex C.2.5, Step 0:b) "pre-load TENT with presented in <xref target="ISO10589" format="default"/>, Annex C.2.5,
the local adjacency database", the suppressed adjacency MUST NOT be Step 0:b) "pre-load TENT with
the local adjacency database", the suppressed adjacency <bcp14>MUST NO
T</bcp14> be
loaded into TENT.</t> loaded into TENT.</t>
</section> </section>
<section numbered="true" toc="default">
<section title="Use of PR and PA Bits"> <name>Use of PR and PA Bits</name>
<t>The PR bit is used by a router which is planning to initiate a <t>The PR bit is used by a router that is planning to initiate a
restart to signal to its neighbors that it will be restarting. The restart to signal to its neighbors that it will be restarting. The
router sending an IIH with PR bit set SHOULD set the "remaining router sending an IIH with PR bit set <bcp14>SHOULD</bcp14> set the Re
time" to a value greater than the expected control plane restart maining
time. The PR bit SHOULD remain set in IIHs until the restart is Time to a value greater than the expected control-plane restart
time. The PR bit <bcp14>SHOULD</bcp14> remain set in IIHs until the re
start is
initiated.</t> initiated.</t>
<t>The PA bit is sent by the neighbor of a router planning to <t>The PA bit is sent by the neighbor of a router planning to
restart to acknowledge receipt of a restart TLV with the PR bit restart to acknowledge receipt of a Restart TLV with the PR bit
set.</t> set.</t>
<t>When the neighbor of a router planning a restart receives an IIH <t>When the neighbor of a router planning a restart receives an IIH
with the restart TLV having the PR bit set, if there exists on this with the Restart TLV having the PR bit set, if there exists on this
interface an adjacency in state "UP" with the same System ID, and in interface an adjacency in the UP state with the same System ID and, in
the case of a LAN circuit, with the same source LAN address, the case of a LAN circuit, with the same source LAN address,
then:</t> then:</t>
<ol spacing="normal" type="a">
<t><list style="letters"> <li>if this is the first IIH with the PR bit set that this system
<t>if this is the first IIH with the PR bit set that this system
has received associated with this adjacency, then the adjacency has received associated with this adjacency, then the adjacency
is marked as being in "Planned Restart state" and the adjacency is marked as being in Planned Restart State and the adjacency
holding time is refreshed -- otherwise, the holding time is not Holding Time is refreshed -- otherwise, the Holding Time is not
refreshed. The holding time SHOULD be set to the "remaining refreshed. The Holding Time <bcp14>SHOULD</bcp14> be set to the Re
time" specified in the received IIH with PR set. The "remaining maining
time" transmitted according to (b) below MUST reflect the actual Time specified in the received IIH with PR set. The Remaining
Time transmitted according to (b) below <bcp14>MUST</bcp14> reflec
t the actual
time after which the adjacency will now expire. Receipt of an time after which the adjacency will now expire. Receipt of an
IIH with the PR bit reset will clear the "Planned Restart state" IIH with the PR bit reset will clear the Planned Restart State
and cause the receiving router to set the adjacency hold time to and cause the receiving router to set the adjacency Holding Time t
o
the locally configured value. This procedure allows the router the locally configured value. This procedure allows the router
planning a restart to cause the neighbor to maintain the planning a restart to cause the neighbor to maintain the
adjacency long enough for restart to successfully complete. adjacency long enough for restart to successfully complete.
Whether or not an adjacency is marked as being in "Planned Whether or not an adjacency is marked as being in Planned
Restart state" has no effect on adjacency state transitions.</t> Restart State has no effect on adjacency state transitions.</li>
<li>immediately (i.e., without waiting for any currently running
<t>immediately (i.e., without waiting for any currently running
timer interval to expire, but with a small random delay of a few timer interval to expire, but with a small random delay of a few
tens of milliseconds on LANs to avoid "storms") transmit over tens of milliseconds on LANs to avoid "storms") transmit over
the corresponding interface an IIH including the restart TLV the corresponding interface an IIH including the Restart TLV
with the PR bit clear and the PA bit set. The "Remaining Time" with the PR bit clear and the PA bit set. The Remaining Time
MUST be set to the current time (in seconds) before the holding <bcp14>MUST</bcp14> be set to the current time (in seconds) before
the holding
timer on this adjacency is due to expire. If the corresponding timer on this adjacency is due to expire. If the corresponding
interface is a LAN interface, then the Restarting Neighbor interface is a LAN interface, then the Restarting Neighbor
System ID SHOULD be set to the System ID of the router from System ID <bcp14>SHOULD</bcp14> be set to the System ID of the rou ter from
which the IIH with the PR bit set was received. This is required which the IIH with the PR bit set was received. This is required
to correctly associate the acknowledgement and holding time in to correctly associate the acknowledgement and Holding Time in
the case where multiple systems on a LAN are planning a restart the case where multiple systems on a LAN are planning a restart
at approximately the same time.</t> at approximately the same time.</li>
</list></t> </ol>
<t>NOTE: Receipt of an IIH with PA bit set indicates to the router <t>NOTE: Receipt of an IIH with PA bit set indicates to the router
planning a restart that the neighbor is aware of the planned restart planning a restart that the neighbor is aware of the planned restart
and - in the absence of topology changes as described below - will and -- in the absence of topology changes as described below -- will
maintain the adjacency for the "remaining time" included in the IIH maintain the adjacency for the Remaining Time included in the IIH
with PA set.</t> with PA set.</t>
<t>By definition, a restarting router maintains forwarding state <t>By definition, a restarting router maintains forwarding state
across the control plane restart (see Section 2). But while a across the control-plane restart (see <xref target="conventions"/>). B
control plane restart is in progress it is expected that the ut while a
control-plane restart is in progress, it is expected that the
restarting router will be unable to respond to topology changes. It restarting router will be unable to respond to topology changes. It
is therefore useful to signal a planned restart so that the is therefore useful to signal a planned restart so that the
neighbors of the restarting router can determine whether it is safe neighbors of the restarting router can determine whether it is safe
to maintain the adjacency if other topology changes occur prior to to maintain the adjacency if other topology changes occur prior to
the completion of the restart. Signalling a planned restart in the the completion of the restart. Signaling a planned restart in the
absence of maintained forwarding plane state is likely to lead to absence of maintained forwarding-plane state is likely to lead to
significant traffic loss and MUST NOT be done.</t> significant traffic loss and <bcp14>MUST NOT</bcp14> be done.</t>
<t>Neighbors of the router that have signaled planned restart <bcp14>S
<t>Neighbors of the router which has signaled planned restart SHOULD HOULD</bcp14>
maintain the adjacency in a planned restart state until it receives maintain the adjacency in a Planned Restart State until it receives
an IIH with the RR bit set, receives an IIH with both PR and RR bits an IIH with the RR bit set, it receives an IIH with both PR and RR bit
clear, or the adjacency holding time expires - whichever occurs s
first. Neighbors which choose not to follow the recommended behavior clear, or the adjacency Holding Time expires -- whichever occurs
first. Neighbors that choose not to follow the recommended behavior
need to consider the impact on traffic delivery of not using the need to consider the impact on traffic delivery of not using the
restarting router for forwarding traffic during the restart restarting router for forwarding traffic during the restart
period.</t> period.</t>
<t>While the adjacency is in Planned Restart State, some or all of
<t>While the adjacency is in planned restart state some or all of the following actions <bcp14>MAY</bcp14> be taken:</t>
the following actions MAY be taken:</t> <ol spacing="normal" type="a">
<li>If additional topology changes occur, the adjacency that is
<t><list style="letters"> in Planned Restart State <bcp14>MAY</bcp14> be brought down even t
<t>if additional topology changes occur, the adjacency which is hough the
in planned restart state MAY be brought down even though the Holding Time has not yet expired. Given that the neighbor that has
hold time has not yet expired. Given that the neighbor which has
signaled a planned restart is not expected to update its signaled a planned restart is not expected to update its
forwarding plane in response to signalling of the topology forwarding plane in response to signaling of the topology
changes (since it is restarting) traffic which transits that changes (since it is restarting) traffic that transits that
node is at risk of being improperly forwarded. On a LAN circuit, node is at risk of being improperly forwarded. On a LAN circuit,
if the router in planned restart state is the DIS at any if the router in Planned Restart State is the DIS at any
supported level, the adjacency(ies) SHOULD be brought down supported level, the adjacency or adjacencies <bcp14>SHOULD</bcp14
whenever any LSP update is either generated or received, so as > be brought down
whenever any LSP update is either generated or received so as
to trigger a new DIS election. Failure to do so will compromise to trigger a new DIS election. Failure to do so will compromise
the reliability of the Update Process on that circuit. What the reliability of the update process on that circuit. What
other criteria are used to determine what topology changes will other criteria are used to determine what topology changes will
trigger bringing the adjacency down is a local implementation trigger bringing the adjacency down is a local implementation
decision.</t> decision.</li>
<li>If a Bidirectional Forwarding Detection (BFD) <xref target="RFC5
<t>if a BFD <xref target="RFC5880"/> session to the neighbor 880" format="default"/> Session to the neighbor
which signals a planned restart is in the UP state and that signals a planned restart is in the UP state and
subsequently goes DOWN, the event MAY be ignored since it is subsequently goes down, the event <bcp14>MAY</bcp14> be ignored si
nce it is
possible this is an expected side effect of the restart. Use of possible this is an expected side effect of the restart. Use of
the Control Plane Independent state as signalled in BFD control the Control-Plane Independent state as signaled in BFD control
packets SHOULD be considered in the decision to ignore a BFD packets <bcp14>SHOULD</bcp14> be considered in the decision to ign
Session DOWN event.</t> ore a BFD
Session DOWN event.</li>
<t>on a Point-to-Point circuit, transmission of LSPs, CSNPs, and <li>On a Point-to-Point circuit, transmission of LSPs, CSNPs, and
PSNPs MAY be suppressed. It is expected that the PDUs will not Partial Sequence Number PDU (PSNPs) <bcp14>MAY</bcp14> be suppress
be received.</t> ed. It is expected that the PDUs will not
</list></t> be received.</li>
</ol>
<t>Use of the PR bit provides a means to safely support restart <t>Use of the PR bit provides a means to safely support restart
periods which are significantly longer than standard holdtimes.</t> periods that are significantly longer than standard Holding Times.</t>
</section> </section>
</section> </section>
<section numbered="true" toc="default">
<section title="Adjacency (Re)Acquisition"> <name>Adjacency (Re)Acquisition</name>
<t>Adjacency (re)acquisition is the first step in (re)initialization. <t>Adjacency (re)acquisition is the first step in (re)initialization.
Restarting and starting routers will make use of the RR bit in the Restarting and starting routers will make use of the RR bit in the
restart TLV, though each will use it at different stages of the Restart TLV, though each will use it at different stages of the
(re)start procedure.</t> (re)start procedure.</t>
<section numbered="true" toc="default" anchor="adjacencyreacqsection">
<section title="Adjacency Reacquisition during Restart"> <name>Adjacency Reacquisition during Restart</name>
<t>The restarting router explicitly notifies its neighbor that the <t>The restarting router explicitly notifies its neighbor that the
adjacency is being reacquired, and hence that it SHOULD NOT adjacency is being reacquired and, hence, that it <bcp14>SHOULD NOT</b cp14>
reinitialize the adjacency. This is achieved by setting the RR bit reinitialize the adjacency. This is achieved by setting the RR bit
in the restart TLV. When the neighbor of a restarting router in the Restart TLV. When the neighbor of a restarting router
receives an IIH with the restart TLV having the RR bit set, if there receives an IIH with the Restart TLV having the RR bit set, if there
exists on this interface an adjacency in state "UP" with the same exists on this interface an adjacency in the UP state with the same
System ID, and in the case of a LAN circuit, with the same source System ID and, in the case of a LAN circuit, with the same source
LAN address, then the procedures described in Section 3.2.1 are LAN address, then the procedures described in <xref target="useofrrrab
itssection"/> are
followed.</t> followed.</t>
<t>A router that does not support the restart capability will ignore <t>A router that does not support the restart capability will ignore
the restart TLV and reinitialize the adjacency as normal, returning the Restart TLV and reinitialize the adjacency as normal, returning
an IIH without the restart TLV.</t> an IIH without the Restart TLV.</t>
<t>On restarting, a router initializes the timer T3, starts the <t>On restarting, a router initializes the timer T3, starts the
timer T2 for each LSPDB, and for each interface (and in the case of timer T2 for each LSPDB, and for each interface (and in the case of
a LAN circuit, for each level) starts the timer T1 and transmits an a LAN circuit, for each level) starts the timer T1 and transmits an
IIH containing the restart TLV with the RR bit set.</t> IIH containing the Restart TLV with the RR bit set.</t>
<t>On a Point-to-Point circuit, the restarting router <bcp14>SHOULD</b
<t>On a Point-to-Point circuit, the restarting router SHOULD set the cp14> set the
"Adjacency Three-Way State" to "Init", because the receipt of the "Adjacency Three-Way State" to "Init", because the receipt of the
acknowledging IIH (with RA set) MUST cause the adjacency to enter acknowledging IIH (with RA set) <bcp14>MUST</bcp14> cause the adjacenc
the "UP" state immediately.</t> y to enter
the UP state immediately.</t>
<t>On a LAN circuit, the LAN-ID assigned to the circuit SHOULD be <t>On a LAN circuit, the LAN-ID assigned to the circuit <bcp14>SHOULD<
/bcp14> be
the same as that used prior to the restart. In particular, for any the same as that used prior to the restart. In particular, for any
circuits for which the restarting router was previously DIS, the use circuits for which the restarting router was previously DIS, the use
of a different LAN-ID would necessitate the generation of a new set of a different LAN-ID would necessitate the generation of a new set
of pseudonode LSPs, and corresponding changes in all the LSPs of pseudonode LSPs and corresponding changes in all the LSPs
referencing them from other routers on the LAN. By preserving the referencing them from other routers on the LAN. By preserving the
LAN-ID across the restart, this churn can be prevented. To enable a LAN-ID across the restart, this churn can be prevented. To enable a
restarting router to learn the LAN-ID used prior to restart, the restarting router to learn the LAN-ID used prior to restart, the
LAN-ID specified in an IIH with RR set MUST be ignored.</t> LAN-ID specified in an IIH with RR set <bcp14>MUST</bcp14> be ignored.
</t>
<t>Transmission of "normal IIHs" is inhibited until the conditions <t>Transmission of "normal IIHs" is inhibited until the conditions
described below are met (in order to avoid causing an unnecessary described below are met (in order to avoid causing an unnecessary
adjacency initialization). Upon expiry of the timer T1, it is adjacency initialization). Upon expiry of the timer T1, it is
restarted and the IIH is retransmitted as above.</t> restarted and the IIH is retransmitted as above.</t>
<t>When a restarting router receives an IIH a local adjacency is <t>When a restarting router receives an IIH a local adjacency is
established as usual, and if the IIH contains a restart TLV with the established as usual, and if the IIH contains a Restart TLV with the
RA bit set (and on LAN circuits with a Restart Neighbor System ID RA bit set (and on LAN circuits with a Restart Neighbor System ID
that matches that of the local system), the receipt of the that matches that of the local system), the receipt of the
acknowledgement over that interface is noted. When the RA bit is set acknowledgement over that interface is noted. When the RA bit is set
and the state of the remote adjacency is "UP", then the timer T3 is and the state of the remote adjacency is UP, then the timer T3 is
set to the minimum of its current value and the value of the set to the minimum of its current value and the value of the
"Remaining Time" field in the received IIH.</t> Remaining Time field in the received IIH.</t>
<t>On a Point-to-Point link, receipt of an IIH not containing the <t>On a Point-to-Point link, receipt of an IIH not containing the
restart TLV is also treated as an acknowledgement, since it Restart TLV is also treated as an acknowledgement, since it
indicates that the neighbor is not restart capable. However, since indicates that the neighbor is not restart capable. However, since
no CSNP is guaranteed to be received over this interface, the timer no CSNP is guaranteed to be received over this interface, the timer
T1 is cancelled immediately without waiting for a complete set of T1 is canceled immediately without waiting for a complete set of
CSNPs. Synchronization may therefore be deemed complete even though CSNPs. Synchronization may therefore be deemed complete even though
there are some LSPs which are held (only) by this neighbor (see there are some LSPs that are held (only) by this neighbor (see
Section 3.4). In this case, we also want to be certain that the <xref target="dbsyncsection"/>). In this case, we also want to be cert
ain that the
neighbor will reinitialize the adjacency in order to guarantee that neighbor will reinitialize the adjacency in order to guarantee that
the SRMflags have been set on its database, thus ensuring eventual the SRMflags have been set on its database, thus ensuring eventual
LSPDB synchronization. This is guaranteed to happen except in the LSPDB synchronization. This is guaranteed to happen except in the
case where the Adjacency Three-Way State in the received IIH is "UP" case where the Adjacency Three-Way State in the received IIH is UP
and the Neighbor Extended Local Circuit ID matches the extended and the Neighbor Extended Local Circuit ID matches the Extended
local circuit ID assigned by the restarting router. In this case, Local Circuit ID assigned by the restarting router. In this case,
the restarting router MUST force the adjacency to reinitialize by the restarting router <bcp14>MUST</bcp14> force the adjacency to reini
setting the local Adjacency Three-Way State to "DOWN" and sending a tialize by
setting the local Adjacency Three-Way State to DOWN and sending a
normal IIH.</t> normal IIH.</t>
<t>In the case of a LAN interface, receipt of an IIH not containing <t>In the case of a LAN interface, receipt of an IIH not containing
the restart TLV is unremarkable since synchronization can still the Restart TLV is unremarkable since synchronization can still
occur so long as at least one of the non-restarting neighboring occur so long as at least one of the non-restarting neighboring
routers on the LAN supports restart. Therefore, T1 continues to run routers on the LAN supports restart. Therefore, T1 continues to run
in this case. If none of the neighbors on the LAN are restart in this case. If none of the neighbors on the LAN are restart
capable, T1 will eventually expire after the locally defined number capable, T1 will eventually expire after the locally defined number
of retries.</t> of retries.</t>
<t>In the case of a Point-to-Point circuit, the LocalCircuitID and
<t>In the case of a Point-to-Point circuit, the "LocalCircuitID" and Extended Local Circuit ID information contained in the IIH can be
"Extended Local Circuit ID" information contained in the IIH can be
used immediately to generate an IIH containing the correct three-way used immediately to generate an IIH containing the correct three-way
handshake information. The presence of "Neighbor Extended Local handshake information. The presence of Neighbor Extended Local
Circuit ID" information that does not match the value currently in Circuit ID information that does not match the value currently in
use by the local system is ignored (since the IIH may have been use by the local system is ignored (since the IIH may have been
transmitted before the neighbor had received the new value from the transmitted before the neighbor had received the new value from the
restarting router), but the adjacency remains in the initializing restarting router), but the adjacency remains in the initializing
state until the correct information is received.</t> state until the correct information is received.</t>
<t>In the case of a LAN circuit, the source neighbor information <t>In the case of a LAN circuit, the source neighbor information
(e.g., SNPAAddress) is recorded and used for adjacency establishment (e.g., SNPAAddress) is recorded and used for adjacency establishment
and maintenance as normal.</t> and maintenance as normal.</t>
<t>When BOTH a complete set of CSNPs (for each active level, in the <t>When BOTH a complete set of CSNPs (for each active level, in the
case of a Point-to-Point circuit) and an acknowledgement have been case of a Point-to-Point circuit) and an acknowledgement have been
received over the interface, the timer T1 is cancelled.</t> received over the interface, the timer T1 is canceled.</t>
<t>Once the timer T1 has been canceled, subsequent IIHs are
<t>Once the timer T1 has been cancelled, subsequent IIHs are transmitted according to the normal algorithms but including the
transmitted according to the normal algorithms, but including the Restart TLV with both RR and RA clear.</t>
restart TLV with both RR and RA clear.</t>
<t>If a LAN contains a mixture of systems, only some of which <t>If a LAN contains a mixture of systems, only some of which
support the new algorithm, database synchronization is still support the new algorithm, database synchronization is still
guaranteed, but the "old" systems will have reinitialized their guaranteed, but the "old" systems will have reinitialized their
adjacencies.</t> adjacencies.</t>
<t>If an interface is active but does not have any neighboring
<t>If an interface is active, but does not have any neighboring
router reachable over that interface, the timer T1 would never be router reachable over that interface, the timer T1 would never be
cancelled, and according to Section 3.4.1.1, the SPF would never be canceled, and according to <xref target="restartingsection"/>, the SPF
run. Therefore, timer T1 is cancelled after some predetermined would never be
number of expirations (which MAY be 1).</t> run. Therefore, timer T1 is canceled after some predetermined
number of expirations (which <bcp14>MAY</bcp14> be 1).</t>
</section> </section>
<section numbered="true" toc="default" anchor="adjacencyacqsection">
<section title="Adjacency Acquisition during Start"> <name>Adjacency Acquisition during Start</name>
<t>The starting router wants to ensure that in the event that a <t>The starting router wants to ensure that in the event that a
neighboring router has an adjacency to the starting router in the neighboring router has an adjacency to the starting router in the
"UP" state (from a previous incarnation of the starting router), UP state (from a previous incarnation of the starting router),
this adjacency is reinitialized. The starting router also wants this adjacency is reinitialized. The starting router also wants
neighboring routers to suppress advertisement of an adjacency to the neighboring routers to suppress advertisement of an adjacency to the
starting router until LSP database synchronization is achieved. This starting router until LSP database synchronization is achieved. This
is achieved by sending IIHs with the RR bit clear and the SA bit set is achieved by sending IIHs with the RR bit clear and the SA bit set
in the restart TLV. The RR bit remains clear and the SA bit remains in the Restart TLV. The RR bit remains clear and the SA bit remains
set in subsequent transmissions of IIHs until the adjacency has set in subsequent transmissions of IIHs until the adjacency has
reached the "UP" state and the initial T1 timer interval (see below) reached the UP state and the initial T1 timer interval (see below)
has expired.</t> has expired.</t>
<t>Receipt of an IIH with the RR bit clear will result in the <t>Receipt of an IIH with the RR bit clear will result in the
neighboring router utilizing normal operation of the adjacency state neighboring router utilizing normal operation of the adjacency state
machine. This will ensure that any old adjacency on the neighboring machine. This will ensure that any old adjacency on the neighboring
router will be reinitialized.</t> router will be reinitialized.</t>
<t>Upon receipt of an IIH with the SA bit set, the behavior <t>Upon receipt of an IIH with the SA bit set, the behavior
described in Section 3.2.2 is followed.</t> described in <xref target="useofsabitsection"/> is followed.</t>
<t>Upon starting, a router starts timer T2 for each LSPDB.</t> <t>Upon starting, a router starts timer T2 for each LSPDB.</t>
<t>For each interface (and in the case of a LAN circuit, for each <t>For each interface (and in the case of a LAN circuit, for each
level), when an adjacency reaches the "UP" state, the starting level), when an adjacency reaches the UP state, the starting
router starts a timer T1 and transmits an IIH containing the restart router starts a timer T1 and transmits an IIH containing the restart
TLV with the RR bit clear and SA bit set. Upon expiry of the timer TLV with the RR bit clear and SA bit set. Upon expiry of the timer
T1, it is restarted and the IIH is retransmitted with both RR and SA T1, it is restarted and the IIH is retransmitted with both RR and SA
bits set (only the RR bit has changed state from earlier IIHs).</t> bits set (only the RR bit has changed state from earlier IIHs).</t>
<t>Upon receipt of an IIH with the RR bit set (regardless of whether <t>Upon receipt of an IIH with the RR bit set (regardless of whether
or not the SA bit is set), the behavior described in Section 3.2.1 or not the SA bit is set), the behavior described in <xref target="use ofrrrabitssection"/>
is followed.</t> is followed.</t>
<t>When an IIH is received by the starting router and the IIH <t>When an IIH is received by the starting router and the IIH
contains a restart TLV with the RA bit set (and on LAN circuits with contains a Restart TLV with the RA bit set (and on LAN circuits with
a Restart Neighbor System ID that matches that of the local system), a Restart Neighbor System ID that matches that of the local system),
the receipt of the acknowledgement over that interface is noted.</t> the receipt of the acknowledgement over that interface is noted.</t>
<t>On a Point-to-Point link, receipt of an IIH not containing the <t>On a Point-to-Point link, receipt of an IIH not containing the
restart TLV is also treated as an acknowledgement, since it Restart TLV is also treated as an acknowledgement, since it
indicates that the neighbor is not restart capable. Since the indicates that the neighbor is not restart capable. Since the
neighbor will have reinitialized the adjacency, this guarantees that neighbor will have reinitialized the adjacency, this guarantees that
SRMflags have been set on its database, thus ensuring eventual LSPDB SRMflags have been set on its database, thus ensuring eventual LSPDB
synchronization. However, since no CSNP is guaranteed to be received synchronization. However, since no CSNP is guaranteed to be received
over this interface, the timer T1 is cancelled immediately without over this interface, the timer T1 is canceled immediately without
waiting for a complete set of CSNPs. Synchronization may therefore waiting for a complete set of CSNPs. Synchronization may therefore
be deemed complete even though there are some LSPs that are held be deemed complete even though there are some LSPs that are held
(only) by this neighbor (see Section 3.4).</t> (only) by this neighbor (see <xref target="dbsyncsection"/>).</t>
<t>In the case of a LAN interface, receipt of an IIH not containing <t>In the case of a LAN interface, receipt of an IIH not containing
the restart TLV is unremarkable since synchronization can still the Restart TLV is unremarkable since synchronization can still
occur so long as at least one of the non-restarting neighboring occur so long as at least one of the non-restarting neighboring
routers on the LAN supports restart. Therefore, T1 continues to run routers on the LAN supports restart. Therefore, T1 continues to run
in this case. If none of the neighbors on the LAN are restart in this case. If none of the neighbors on the LAN are restart
capable, T1 will eventually expire after the locally defined number capable, T1 will eventually expire after the locally defined number
of retries. The usual operation of the update process will ensure of retries. The usual operation of the update process will ensure
that synchronization is eventually achieved.</t> that synchronization is eventually achieved.</t>
<t>When BOTH a complete set of CSNPs (for each active level, in the <t>When BOTH a complete set of CSNPs (for each active level, in the
case of a Point-to-Point circuit) and an acknowledgement have been case of a Point-to-Point circuit) and an acknowledgement have been
received over the interface, the timer T1 is cancelled. Subsequent received over the interface, the timer T1 is canceled. Subsequent
IIHs sent by the starting router have the RR and RA bits clear and IIHs sent by the starting router have the RR and RA bits clear and
the SA bit set in the restart TLV.</t> the SA bit set in the Restart TLV.</t>
<t>Timer T1 is canceled after some predetermined number of
<t>Timer T1 is cancelled after some predetermined number of expirations (which <bcp14>MAY</bcp14> be 1).</t>
expirations (which MAY be 1).</t> <t>When the T2 timer(s) are canceled or expire, transmission of
<t>When the T2 timer(s) are cancelled or expire, transmission of
"normal IIHs" will begin.</t> "normal IIHs" will begin.</t>
</section> </section>
<section numbered="true" toc="default">
<section title="Multiple Levels"> <name>Multiple Levels</name>
<t>A router that is operating as both a Level 1 and a Level 2 router <t>A router that is operating as both a Level 1 and a Level 2 router
on a particular interface MUST perform the above operations for each on a particular interface <bcp14>MUST</bcp14> perform the above operat ions for each
level.</t> level.</t>
<t>On a LAN interface, it <bcp14>MUST</bcp14> send and receive both Le
<t>On a LAN interface, it MUST send and receive both Level 1 and vel 1 and
Level 2 IIHs and perform the CSNP synchronizations independently for Level 2 IIHs and perform the CSNP synchronizations independently for
each level.</t> each level.</t>
<t>On a Point-to-Point interface, only a single IIH (indicating <t>On a Point-to-Point interface, only a single IIH (indicating
support for both levels) is required, but it MUST perform the CSNP support for both levels) is required, but it <bcp14>MUST</bcp14> perfo rm the CSNP
synchronizations independently for each level.</t> synchronizations independently for each level.</t>
</section> </section>
</section> </section>
<section numbered="true" toc="default" anchor="dbsyncsection">
<section title="Database Synchronization"> <name>Database Synchronization</name>
<t>When a router is started or restarted, it can expect to receive a <t>When a router is started or restarted, it can expect to receive a
complete set of CSNPs over each interface. The arrival of the CSNP(s) complete set of CSNPs over each interface. The arrival of the CSNP(s)
is now guaranteed, since an IIH with the RR bit set will be is now guaranteed, since an IIH with the RR bit set will be
retransmitted until the CSNP(s) are correctly received.</t> retransmitted until the CSNP(s) are correctly received.</t>
<t>The CSNPs describe the set of LSPs that are currently held by each <t>The CSNPs describe the set of LSPs that are currently held by each
neighbor. Synchronization will be complete when all these LSPs have neighbor. Synchronization will be complete when all these LSPs have
been received.</t> been received.</t>
<t>When (re)starting, a router starts an instance of timer T2 for each <t>When (re)starting, a router starts an instance of timer T2 for each
LSPDB as described in Section 3.3.1 or Section 3.3.2. In addition to LSPDB, as described in <xref target="adjacencyreacqsection"/> or <xref t arget="adjacencyacqsection"/>. In addition to
normal processing of the CSNPs, the set of LSPIDs contained in the normal processing of the CSNPs, the set of LSPIDs contained in the
first complete set of CSNPs received over each interface is recorded, first complete set of CSNPs received over each interface is recorded,
together with their remaining lifetime. In the case of a LAN together with their remaining lifetime. In the case of a LAN
interface, a complete set of CSNPs MUST consist of CSNPs received from interface, a complete set of CSNPs <bcp14>MUST</bcp14> consist of CSNPs received from
neighbors that are not restarting. If there are multiple interfaces on neighbors that are not restarting. If there are multiple interfaces on
the (re)starting router, the recorded set of LSPIDs is the union of the (re)starting router, the recorded set of LSPIDs is the union of
those received over each interface. LSPs with a remaining lifetime of those received over each interface. LSPs with a remaining lifetime of
zero are NOT so recorded.</t> zero are NOT so recorded.</t>
<t>As LSPs are received (by the normal operation of the update <t>As LSPs are received (by the normal operation of the update
process) over any interface, the corresponding LSPID entry is removed process) over any interface, the corresponding LSPID entry is removed
(it is also removed if an LSP arrives before the CSNP containing the (it is also removed if an LSP arrives before the CSNP containing the
reference). When an LSPID has been held in the list for its indicated reference). When an LSPID has been held in the list for its indicated
remaining lifetime, it is removed from the list. When the list of remaining lifetime, it is removed from the list. When the list of
LSPIDs is empty and the timer T1 has been cancelled for all the LSPIDs is empty and the timer T1 has been canceled for all the
interfaces that have an adjacency at this level, the timer T2 is interfaces that have an adjacency at this level, the timer T2 is
cancelled.</t> canceled.</t>
<t>At this point, the local database is guaranteed to contain all the <t>At this point, the local database is guaranteed to contain all the
LSP(s) (either the same sequence number or a more recent sequence LSP(s) (either the same sequence number or a more recent sequence
number) that were present in the neighbors' databases at the time of number) that were present in the neighbors' databases at the time of
(re)starting. LSPs that arrived in a neighbor's database after the (re)starting. LSPs that arrived in a neighbor's database after the
time of (re)starting may or may not be present, but the normal time of (re)starting may or may not be present, but the normal
operation of the update process will guarantee that they will operation of the update process will guarantee that they will
eventually be received. At this point, the local database is deemed to eventually be received. At this point, the local database is deemed to
be "synchronized".</t> be "synchronized".</t>
<t>Since LSPs mentioned in the CSNP(s) with a zero remaining lifetime <t>Since LSPs mentioned in the CSNP(s) with a zero remaining lifetime
are not recorded, and those with a short remaining lifetime are are not recorded and those with a short remaining lifetime are
deleted from the list when the lifetime expires, cancellation of the deleted from the list when the lifetime expires, cancellation of the
timer T2 will not be prevented by waiting for an LSP that will never timer T2 will not be prevented by waiting for an LSP that will never
arrive.</t> arrive.</t>
<section numbered="true" toc="default">
<section title="LSP Generation and Flooding and SPF Computation"> <name>LSP Generation and Flooding and SPF Computation</name>
<t>The operation of a router starting, as opposed to restarting, is <t>The operation of a router starting, as opposed to restarting, is
somewhat different. These two cases are dealt with separately somewhat different. These two cases are dealt with separately
below.</t> below.</t>
<section numbered="true" toc="default" anchor="restartingsection">
<section title="Restarting"> <name>Restarting</name>
<t>In order to avoid causing unnecessary routing churn in other <t>In order to avoid causing unnecessary routing churn in other
routers, it is highly desirable that the router's own LSPs routers, it is highly desirable that the router's own LSPs
generated by the restarting system are the same as those generated by the restarting system are the same as those
previously present in the network (assuming no other changes have previously present in the network (assuming no other changes have
taken place). It is important therefore not to regenerate and taken place). It is important therefore not to regenerate and
flood the LSPs until all the adjacencies have been re-established flood the LSPs until all the adjacencies have been reestablished
and any information required for propagation into the local LSPs and any information required for propagation into the local LSPs
is fully available. Ideally, the information is loaded into the is fully available. Ideally, the information is loaded into the
LSPs in a deterministic way, such that the same information occurs LSPs in a deterministic way, such that the same information occurs
in the same place in the same LSP (and hence the LSPs are in the same place in the same LSP (and hence the LSPs are
identical to their previous versions). If this can be achieved, identical to their previous versions). If this can be achieved,
the new versions may not even cause SPF to be run in other the new versions may not even cause SPF to be run in other
systems. However, provided the same information is included in the systems. However, provided the same information is included in the
set of LSPs (albeit in a different order, and possibly different set of LSPs (albeit in a different order, and possibly different
LSPs), the result of running the SPF will be the same and will not LSPs), the result of running the SPF will be the same and will not
cause churn to the forwarding tables.</t> cause churn to the forwarding tables.</t>
skipping to change at line 784 skipping to change at line 706
and any information required for propagation into the local LSPs and any information required for propagation into the local LSPs
is fully available. Ideally, the information is loaded into the is fully available. Ideally, the information is loaded into the
LSPs in a deterministic way, such that the same information occurs LSPs in a deterministic way, such that the same information occurs
in the same place in the same LSP (and hence the LSPs are in the same place in the same LSP (and hence the LSPs are
identical to their previous versions). If this can be achieved, identical to their previous versions). If this can be achieved,
the new versions may not even cause SPF to be run in other the new versions may not even cause SPF to be run in other
systems. However, provided the same information is included in the systems. However, provided the same information is included in the
set of LSPs (albeit in a different order, and possibly different set of LSPs (albeit in a different order, and possibly different
LSPs), the result of running the SPF will be the same and will not LSPs), the result of running the SPF will be the same and will not
cause churn to the forwarding tables.</t> cause churn to the forwarding tables.</t>
<t>In the case of a restarting router, none of the router's own <t>In the case of a restarting router, none of the router's own
LSPs are transmitted, nor are the router's own forwarding tables LSPs are transmitted, nor are the router's own forwarding tables
updated while the timer T3 is running.</t> updated while the timer T3 is running.</t>
<t>Redistribution of inter-level information <bcp14>MUST</bcp14> be
<t>Redistribution of inter-level information MUST be regenerated regenerated
before this router's LSP is flooded to other nodes. Therefore, the before this router's LSP is flooded to other nodes. Therefore, the
Level-n non-pseudonode LSP(s) MUST NOT be flooded until the other Level-n non-pseudonode LSP(s) <bcp14>MUST NOT</bcp14> be flooded unt il the other
level's T2 timer has expired and its SPF has been run. This level's T2 timer has expired and its SPF has been run. This
ensures that any inter-level information that is to be propagated ensures that any inter-level information that is to be propagated
can be included in the Level-n LSP(s).</t> can be included in the Level-n LSP(s).</t>
<t>During this period, if one of the router's own (including <t>During this period, if one of the router's own (including
pseudonodes) LSPs is received, which the local router does not pseudonodes) LSPs is received, which the local router does not
currently have in its own database, it is NOT purged. Under normal currently have in its own database, it is NOT purged. Under normal
operation, such an LSP would be purged, since the LSP clearly operation, such an LSP would be purged, since the LSP clearly
should not be present in the global LSP database. However, in the should not be present in the global LSP database. However, in the
present circumstances, this would be highly undesirable, because present circumstances, this would be highly undesirable, because
it could cause premature removal of a router's own LSP -- and it could cause premature removal of a router's own LSP -- and
hence churn in remote routers. Even if the local system has one or hence churn in remote routers. Even if the local system has one or
more of the router's own LSPs (which it has generated, but not yet more of the router's own LSPs (which it has generated but not yet
transmitted), it is still not valid to compare the received LSP transmitted), it is still not valid to compare the received LSP
against this set, since it may be that as a result of propagation against this set, since it may be that as a result of propagation
between Level 1 and Level 2 (or vice versa), a further router's between Level 1 and Level 2 (or vice versa), a further router's
own LSP will need to be generated when the LSP databases have own LSP will need to be generated when the LSP databases have
synchronized.</t> synchronized.</t>
<t>During this period, a restarting router <bcp14>SHOULD</bcp14> sen
<t>During this period, a restarting router SHOULD send CSNPs as it d CSNPs as it
normally would. Information about the router's own LSPs MAY be normally would. Information about the router's own LSPs <bcp14>MAY</
included, but if it is included it MUST be based on LSPs that have bcp14> be
included, but if it is included, it <bcp14>MUST</bcp14> be based on
LSPs that have
been received, not on versions that have been generated (but not been received, not on versions that have been generated (but not
yet transmitted). This restriction is necessary to prevent yet transmitted). This restriction is necessary to prevent
premature removal of an LSP from the global LSP database.</t> premature removal of an LSP from the global LSP database.</t>
<t>When the timer T2 expires or is canceled, indicating that
<t>When the timer T2 expires or is cancelled indicating that
synchronization for that level is complete, the SPF for that level synchronization for that level is complete, the SPF for that level
is run in order to derive any information that is required to be is run in order to derive any information that is required to be
propagated to another level, but the forwarding tables are not yet propagated to another level, but the forwarding tables are not yet
updated.</t> updated.</t>
<t>Once the other level's SPF has run and any inter-level <t>Once the other level's SPF has run and any inter-level
propagation has been resolved, the router's own LSPs can be propagation has been resolved, the router's own LSPs can be
generated and flooded. Any own LSPs that were previously ignored, generated and flooded. Any own LSPs that were previously ignored,
but that are not part of the current set of own LSPs (including but that are not part of the current set of own LSPs (including
pseudonodes), MUST then be purged. Note that it is possible that a pseudonodes), <bcp14>MUST</bcp14> then be purged. Note that it is po
Designated Router change may have taken place, and consequently ssible that a
the router SHOULD purge those pseudonode LSPs that it previously Designated Router change may have taken place and, consequently,
owned, but that are now no longer part of its set of pseudonode the router <bcp14>SHOULD</bcp14> purge those pseudonode LSPs that it
previously
owned but that are now no longer part of its set of pseudonode
LSPs.</t> LSPs.</t>
<t>When all the T2 timers have expired or been canceled, the
<t>When all the T2 timers have expired or been cancelled, the timer T3 is canceled, and the local forwarding tables are
timer T3 is cancelled and the local forwarding tables are
updated.</t> updated.</t>
<t>If the timer T3 expires before all the T2 timers have expired <t>If the timer T3 expires before all the T2 timers have expired
or been cancelled, this indicates that the synchronization process or been canceled, this indicates that the synchronization process
is taking longer than the minimum holding time of the neighbors. is taking longer than the minimum Holding Time of the neighbors.
The router's own LSP(s) for levels that have not yet completed The router's own LSP(s) for levels that have not yet completed
their first SPF computation are then flooded with the overload bit their first SPF computation are then flooded with the overload bit
set to indicate that the router's LSPDB is not yet synchronized set to indicate that the router's LSPDB is not yet synchronized
(and therefore other routers MUST NOT compute routes through this (and therefore other routers <bcp14>MUST NOT</bcp14> compute routes through this
router). Normal operation of the update process resumes, and the router). Normal operation of the update process resumes, and the
local forwarding tables are updated. In order to prevent the local forwarding tables are updated. In order to prevent the
neighbor's adjacencies from expiring, IIHs with the normal neighbor's adjacencies from expiring, IIHs with the normal
interface value for the holding time are transmitted over all interface value for the Holding Time are transmitted over all
interfaces with neither RR nor RA set in the restart TLV. This interfaces with neither RR nor RA set in the Restart TLV. This
will cause the neighbors to refresh their adjacencies. The will cause the neighbors to refresh their adjacencies. The
router's own LSP(s) will continue to have the overload bit set router's own LSP(s) will continue to have the overload bit set
until timer T2 has expired or been cancelled.</t> until timer T2 has expired or been canceled.</t>
</section> </section>
<section numbered="true" toc="default">
<section title="Starting"> <name>Starting</name>
<t>In the case of a starting router, as soon as each adjacency is <t>In the case of a starting router, as soon as each adjacency is
established, and before any CSNP exchanges, the router's own established, and before any CSNP exchanges, the router's own
zeroth LSP is transmitted with the overload bit set. This prevents zeroth LSP is transmitted with the overload bit set. This prevents
other routers from computing routes through the router until it other routers from computing routes through the router until it
has reliably acquired the complete set of LSPs. The overload bit has reliably acquired the complete set of LSPs. The overload bit
remains set in subsequent transmissions of the zeroth LSP (such as remains set in subsequent transmissions of the zeroth LSP (such as
will occur if a previous copy of the router's own zeroth LSP is will occur if a previous copy of the router's own zeroth LSP is
still present in the network) while any timer T2 is running.</t> still present in the network) while any timer T2 is running.</t>
<t>When all the T2 timers have been canceled, the router's own
<t>When all the T2 timers have been cancelled, the router's own LSP(s) <bcp14>MAY</bcp14> be regenerated with the overload bit clear
LSP(s) MAY be regenerated with the overload bit clear (assuming (assuming
the router is not in fact overloaded, and there is no other the router is not in fact overloaded, and there is no other
reason, such as incomplete BGP convergence, to keep the overload reason, such as incomplete BGP convergence, to keep the overload
bit set) and flooded as normal.</t> bit set) and flooded as normal.</t>
<t>Other LSPs owned by this router (including pseudonodes) are <t>Other LSPs owned by this router (including pseudonodes) are
generated and flooded as normal, irrespective of the timer T2. The generated and flooded as normal, irrespective of the timer T2. The
SPF is also run as normal and the Routing Information Base (RIB) SPF is also run as normal and the Routing Information Base (RIB)
and Forwarding Information Base (FIB) updated as routes become and Forwarding Information Base (FIB) updated as routes become
available.</t> available.</t>
<t>To avoid the possible formation of temporary blackholes, the <t>To avoid the possible formation of temporary blackholes, the
starting router sets the SA bit in the restart TLV (as described starting router sets the SA bit in the Restart TLV (as described
in Section 3.3.2) in all IIHs that it sends.</t> in <xref target="adjacencyacqsection"/>) in all IIHs that it sends.<
/t>
<t>When all T2 timers have been cancelled, the starting router <t>When all T2 timers have been canceled, the starting router
MUST transmit IIHs with the SA bit clear.</t> <bcp14>MUST</bcp14> transmit IIHs with the SA bit clear.</t>
</section> </section>
</section> </section>
</section> </section>
</section> </section>
<section numbered="true" toc="default">
<section title="State Tables"> <name>State Tables</name>
<t>This section presents state tables that summarize the behaviors <t>This section presents state tables that summarize the behaviors
described in this document. Other behaviors, in particular adjacency described in this document. Other behaviors, in particular adjacency
state transitions and LSP database update operation, are NOT included in state transitions and LSP database update operations, are NOT included in
the state tables except where this document modifies the behaviors the state tables except where this document modifies the behaviors
described in <xref target="ISO10589"/> and <xref target="RFC5303"/>.</t> described in <xref target="ISO10589" format="default"/> and <xref target="
RFC5303" format="default"/>.</t>
<t>The states named in the columns of the tables below are a mixture of <t>The states named in the columns of the tables below are a mixture of
states that are specific to a single adjacency (ADJ suppressed, ADJ Seen states that are specific to a single adjacency (ADJ suppressed, ADJ Seen
RA, ADJ Seen CSNP) and states that are indicative of the state of the RA, ADJ Seen CSNP) and states that are indicative of the state of the
protocol instance (Running, Restarting, Starting, SPF Wait).</t> protocol instance (Running, Restarting, Starting, SPF Wait).</t>
<t>Three state tables are presented from the point of view of a running <t>Three state tables are presented from the point of view of a running
router, a restarting router, and a starting router.</t> router, a restarting router, and a starting router.</t>
<section numbered="true" toc="default">
<name>Running Router</name>
<section title="Running Router"> <table anchor="table1">
<t><figure> <name>Running Router</name>
<artwork><![CDATA[ Event | Running | ADJ suppr <thead>
essed <tr>
============================================================== <th>Event</th>
RX PR | Set Planned Restart | <th>Running</th>
| state. | <th>ADJ suppressed</th>
| Update hold time </tr>
| Send PA | </thead>
-------------+----------------------+------------------------- <tbody>
RX PR clr | Clear Planned | <tr>
and RR clr | Restart State | <td>RX PR</td>
| Restore holdtime to | <td><t>Set Planned Restart State<br/>
| local value | Update Holding Time<br/>
-------------+----------------------+------------------------- Send PA</t></td>
RX RR | Maintain ADJ State | <td></td>
| Send RA | </tr>
| Set SRM,send CSNP | <tr>
| (Note 1) | <td>RX PR clr and RR clr</td>
| Update Hold Time, | <td><t>Clear Planned Restart State<br/>
| set Restart Mode | Restore Holding Time to local value</t></td>
| (Note 2) | <td></td>
-------------+----------------------+------------------------- </tr>
RX RR clr | Clr Restart mode | <tr>
-------------+----------------------+-------------------------
RX SA | Suppress IS neighbor |
| TLV in LSP(s) |
| Goto ADJ Suppressed |
-------------+----------------------+-------------------------
RX SA clr | |Unsuppress IS neighbor
| | TLV in LSP(s)
| |Goto Running
==============================================================
Note 1: CSNPs are sent by routers in accordance with Section 3.2.1c <td>RX RR</td>
<td>
<t>Maintain ADJ State<br/>
Send RA<br/>
Set SRM, send CSNP (<xref target="note1" format="none">Note 1</xref>)<br/
>
Update Holding Time,<br/> set Restart Mode (<xref target="note2" format="
none">Note 2</xref>)</t>
</td>
<td></td>
</tr>
<tr>
<td>RX RR clr</td>
<td>Clr Restart mode</td>
<td></td>
</tr>
<tr>
<td>RX SA</td>
<td>
<t>Suppress IS neighbor TLV in LSP&wj;(s)<br/>
Goto ADJ Suppressed</t>
</td>
<td></td>
</tr>
<tr>
<td>RX SA clr</td>
<td></td>
<td>
<t>Unsuppress IS neighbor TLV in LSP&wj;(s)<br/>
Goto Running</t>
</td>
</tr>
Note 2: If Restart Mode clear </tbody>
</table>
]]></artwork> <ol type="Note %d:">
</figure></t>
<li anchor="note1">CSNPs are sent by routers in accordance with <xref
target="itemc" format="none">item c</xref> in <xref target="useofrrrabitssecti
on"/></li>
<li anchor="note2">If Restart Mode clear</li>
</ol>
</section> </section>
<section numbered="true" toc="default">
<name>Restarting Router</name>
<section title="Restarting Router"> <table anchor="table2">
<t><figure> <name>Restarting Router</name>
<artwork><![CDATA[ Event | Restarting | ADJ Seen | AD <thead>
J Seen | SPF Wait <tr>
| | RA | CSNP | <th>Event</th>
=================================================================== <th>Restarting</th>
Restart | Send PR | | | <th>ADJ Seen RA</th>
planned | | | | <th>ADJ Seen CSNP</th>
------------+--------------------+-----------+-----------+------------ <th>SPF Wait</th>
Planned | Send PR clr | | | </tr>
restart | | | | </thead>
canceled | | | | <tbody>
------------+--------------------+-----------+-----------+------------ <tr>
RX PA | Proceed with | | | <td>Restart planned</td>
| planned restart | | | <td>Send PR</td>
------------+--------------------+-----------+-----------+------------ <td></td>
Router | Send IIH/RR | | | <td></td>
restarts | ADJ Init | | | <td></td>
| Start T1,T2,T3 | | | </tr>
------------+--------------------+-----------+-----------+------------ <tr>
RX RR | Send RA | | | <td>Planned restart canceled</td>
------------+--------------------+-----------+-----------+------------ <td>Send PR clr</td>
RX RA | Adjust T3 | | Cancel T1 | <td></td>
| Goto ADJ Seen RA | | Adjust T3 | <td></td>
----------- +--------------------+-----------+-----------+------------ <td></td>
RX CSNP set| Goto ADJ Seen CSNP | Cancel T1 | | </tr>
------------+--------------------+-----------+-----------+------------ <tr>
RX IIH w/o | Cancel T1 (Point- | | | <td>RX PA</td>
Restart TLV| to-point only) | | | <td>Proceed with planned restart</td>
------------+--------------------+-----------+-----------+------------ <td></td>
T1 expires | Send IIH/RR |Send IIH/RR|Send IIH/RR| <td></td>
| Restart T1 | Restart T1| Restart T1| <td></td>
------------+--------------------+-----------+-----------+------------ </tr>
T1 expires | Send IIH/ | Send IIH/ | Send IIH/ | <tr>
nth time | normal | normal | normal | <td>Router restarts</td>
------------+--------------------+-----------+-----------+------------ <td>
T2 expires | Trigger SPF | | | <t>Send IIH/RR<br/>
| Goto SPF Wait | | | ADJ Init<br/>
------------+--------------------+-----------+-----------+------------ Start T1, T2, T3</t>
T3 expires | Set overload bit | | | </td>
| Flood local LSPs | | | <td></td>
| Update fwd plane | | | <td></td>
------------+--------------------+-----------+-----------+------------ <td></td>
LSP DB Sync| Cancel T2, and T3 | | | </tr>
| Trigger SPF | | | <tr>
| Goto SPF wait | | | <td>RX RR</td>
------------+--------------------+-----------+-----------+------------ <td>Send RA</td>
All SPF | | | | Clear <td></td>
done | | | | overload bit <td></td>
| | | | Update fwd <td></td>
| | | | plane </tr>
| | | | Flood local <tr>
| | | | LSPs <td>RX RA</td>
| | | | Goto Running <td><t>Adjust T3<br/>
====================================================================== Goto ADJ Seen RA</t></td>
<td></td>
<td><t>Cancel T1<br/>
Adjust T3</t></td>
<td></td>
</tr>
<tr>
<td>RX CSNP set</td>
<td>Goto ADJ Seen CSNP</td>
<td>Cancel T1</td>
<td></td>
<td></td>
</tr>
<tr>
<td>RX IIH w/o Restart TLV</td>
<td>Cancel T1 (Point-to-point only)</td>
<td></td>
<td></td>
<td></td>
</tr>
<tr>
<td>T1 expires</td>
<td>
<t>Send IIH/RR<br/>
Restart T1</t>
</td>
<td>
<t>Send IIH/RR<br/>
Restart T1</t>
</td>
<td>
<t>Send IIH/RR<br/>
Restart T1</t>
</td>
<td></td>
</tr>
<tr>
<td>T1 expires nth time</td>
<td>Send IIH/normal</td>
<td>Send IIH/normal</td>
<td>Send IIH/normal</td>
<td></td>
</tr>
<tr>
<td>T2 expires</td>
<td><t>Trigger SPF<br/>
Goto SPF Wait</t></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr>
<td>T3 expires</td>
<td><t>Set overload bit<br/>
Flood local LSPs<br/>
Update fwd plane</t></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr>
<td>LSP DB Sync</td>
<td><t>Cancel T2 and T3<br/>
Trigger SPF<br/>
Goto SPF wait</t></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr>
<td>All SPF done</td>
<td></td>
<td></td>
<td></td>
<td><t>Clear overload bit<br/>
Update fwd plane<br/>
Flood local LSPs<br/>
Goto Running</t></td>
</tr>
</tbody>
</table>
]]></artwork>
</figure></t>
</section> </section>
<section numbered="true" toc="default">
<name>Starting Router</name>
<section title="Starting Router"> <table anchor="table3">
<t><figure> <name>Starting Router</name>
<artwork><![CDATA[ Event | Starting | ADJ Seen RA| <thead>
ADJ Seen CSNP <tr>
============================================================= <th>Event</th>
Router | Send IIH/SA | | <th>Starting</th>
starts | Start T1,T2 | | <th>ADJ Seen RA</th>
-------------+-------------------+------------+--------------- <th>ADJ Seen CSNP</th>
RX RR | Send RA | | </tr>
-------------+-------------------+------------+--------------- </thead>
RX RA | Goto ADJ Seen RA | | Cancel T1 <tbody>
-------------+-------------------+------------+--------------- <tr>
RX CSNP Set | Goto ADJ Seen CSNP| Cancel T1 | <td>Router starts</td>
-------------+-------------------+------------+--------------- <td><t>Send IIH/SA<br/>
RX IIH w | Cancel T1 | | Start T1 and T2</t></td>
no Restart | (Point-to-Point | | <td></td>
TLV | only) | | <td></td>
-------------+-------------------+------------+--------------- </tr>
ADJ UP | Start T1 | | <tr>
| Send local LSPs | | <td>RX RR</td>
| with overload bit| | <td>Send RA</td>
| set | | <td></td>
-------------+-------------------+------------+--------------- <td></td>
T1 expires | Send IIH/RR |Send IIH/RR | Send IIH/RR </tr>
| and SA | and SA | and SA <tr>
| Restart T1 |Restart T1 | Restart T1 <td>RX RA</td>
-------------+-------------------+------------+--------------- <td>Goto ADJ Seen RA</td>
T1 expires | Send IIH/SA |Send IIH/SA | Send IIH/SA <td></td>
nth time | | | <td>Cancel T1</td>
-------------+-------------------+------------+--------------- </tr>
T2 expires | Clear overload bit| | <tr>
| Send IIH normal | | <td>RX CSNP Set</td>
| Goto Running | | <td>Goto ADJ Seen CSNP</td>
-------------+-------------------+------------+--------------- <td>Cancel T1</td>
LSP DB Sync | Cancel T2 | | <td></td>
| Clear overload bit| | </tr>
| Send IIH normal | | <tr>
============================================================== <td>RX IIH w no Restart TLV</td>
<td>Cancel T1 (Point-to-Point only)</td>
<td></td>
<td></td>
</tr>
<tr>
<td>ADJ UP</td>
<td><t>Start T1<br/>
Send local LSPs with overload bit set</t></td>
<td></td>
<td></td>
</tr>
<tr>
<td>T1 expires</td>
<td>
<t>Send IIH/RR and SA<br/>
Restart T1</t>
</td>
<td><t>Send IIH/RR and SA<br/>
Restart T1</t></td>
<td><t>Send IIH/RR and SA<br/>
Restart T1</t></td>
</tr>
<tr>
<td>T1 expires nth time</td>
<td>Send IIH/SA</td>
<td>Send IIH/SA</td>
<td>Send IIH/SA</td>
</tr>
<tr>
<td>T2 expires</td>
<td><t>Clear overload bit<br/>
Send IIH normal<br/>
Goto Running</t></td>
<td></td>
<td></td>
</tr>
<tr>
<td>LSP DB Sync</td>
<td><t>Cancel T2<br/>
Clear overload bit<br/>
Send IIH normal</t></td>
<td></td>
<td></td>
</tr>
</tbody>
</table>
]]></artwork>
</figure></t>
</section> </section>
</section> </section>
<section anchor="IANA" numbered="true" toc="default">
<section anchor="IANA" title="IANA Considerations"> <name>IANA Considerations</name>
<t>This document defines the following IS-IS TLV that is listed in the <t>This document defines the following IS-IS TLV that is listed in the
IS-IS TLV codepoint registry:</t> "IS-IS TLV Codepoints" registry.</t>
<t><figure> <table anchor="ianatable" align="left">
<artwork><![CDATA[ Type Description IIH L <thead>
SP SNP Purge <tr>
---- ------------------------------ --- --- --- ----- <th>Type</th>
211 Restart TLV y n n n <th>Description</th>
<th>IIH</th>
<th>LSP</th>
<th>SNP</th>
<th>Purge</th>
</tr>
</thead>
<tbody>
<tr>
<td>211</td>
<td>Restart TLV</td>
<td>y</td>
<td>n</td>
<td>n</td>
<td>n</td>
</tr>
</tbody>
</table>
]]></artwork> <t>IANA has updated the entry in registry to point to
</figure>IANA is requested to update the entry in registry to point to
this document.</t> this document.</t>
</section> </section>
<section anchor="Security" numbered="true" toc="default">
<section anchor="Security" title="Security Considerations"> <name>Security Considerations</name>
<t>Any new security issues raised by the procedures in this document <t>Any new security issues raised by the procedures in this document
depend upon the ability of an attacker to inject a false but apparently depend upon the ability of an attacker to inject a false but apparently
valid IIH, the ease/difficulty of which has not been altered.</t> valid IIH, the ease/difficulty of which has not been altered.</t>
<t>If the RR bit is set in a false IIH, neighbors who receive such an <t>If the RR bit is set in a false IIH, neighbors who receive such an
IIH will continue to maintain an existing adjacency in the "UP" state IIH will continue to maintain an existing adjacency in the UP state
and may (re)send a complete set of CSNPs. While the latter action is and may (re)send a complete set of CSNPs. While the latter action is
wasteful, neither action causes any disruption in correct protocol wasteful, neither action causes any disruption in correct protocol
operation.</t> operation.</t>
<t>If the RA bit is set in a false IIH, a (re)starting router that <t>If the RA bit is set in a false IIH, a (re)starting router that
receives such an IIH may falsely believe that there is a neighbor on the receives such an IIH may falsely believe that there is a neighbor on the
corresponding interface that supports the procedures described in this corresponding interface that supports the procedures described in this
document. In the absence of receipt of a complete set of CSNPs on that document. In the absence of receipt of a complete set of CSNPs on that
interface, this could delay the completion of (re)start procedures by interface, this could delay the completion of (re)start procedures by
requiring the timer T1 to time out the locally defined maximum number of requiring the timer T1 to time out the locally defined maximum number of
retries. This behavior is the same as would occur on a LAN where none of retries. This behavior is the same as would occur on a LAN where none of
the (re)starting router's neighbors support the procedures in this the (re)starting router's neighbors support the procedures in this
document and is covered in Sections 3.3.1 and 3.3.2.</t> document and is covered in Sections <xref
target="adjacencyreacqsection" format="counter"/> and <xref
target="adjacencyacqsection" format="counter"/>.</t>
<t>If the SA bit is set in a false IIH, this could cause suppression of <t>If the SA bit is set in a false IIH, this could cause suppression of
the advertisement of an IS neighbor, which could either continue for an the advertisement of an IS neighbor, which could either continue for an
indefinite period or occur intermittently with the result being a indefinite period or occur intermittently with the result being a
possible loss of reachability to some destinations in the network and/or possible loss of reachability to some destinations in the network and/or
increased frequency of LSP flooding and SPF calculation.</t> increased frequency of LSP flooding and SPF calculation.</t>
<t>If the PR bit is set in a false IIH, neighbors who receive such an <t>If the PR bit is set in a false IIH, neighbors who receive such an
IIH could modify the holding time of an existing adjacency IIH could modify the Holding Time of an existing adjacency
inappropriately. In the event of topology changes, the neighbor might inappropriately. In the event of topology changes, the neighbor might
also choose to not flood the topology updates and/or bring the adjacency also choose to not flood the topology updates and/or bring the adjacency
down in the false belief that the forwarding plane of the router down in the false belief that the forwarding plane of the router
identified as the source of the false IIH is not currently processing identified as the source of the false IIH is not currently processing
announced topology changes. This would result in unnecessary forwarding announced topology changes. This would result in unnecessary forwarding
disruption.</t> disruption.</t>
<t>If the PA bit is set in a false IIH, a router that receives such an <t>If the PA bit is set in a false IIH, a router that receives such an
IIH may falsely believe that the neighbor on the corresponding interface IIH may falsely believe that the neighbor on the corresponding interface
supports the planned restart procedures defined in this document. If supports the planned restart procedures defined in this document. If
such a router is planning to restart it might then proceed to initiate a such a router is planning to restart, it might then proceed to initiate a
restart in the false expectation that the neighbor has updated its restart in the false expectation that the neighbor has updated its
holding time as requested. This may result in the neighbor bringing down Holding Time as requested. This may result in the neighbor bringing down
the adjacency while the receiving router is restarting, causing the adjacency while the receiving router is restarting, causing
unnecessary disruption to forwarding.</t> unnecessary disruption to forwarding.</t>
<t>The possibility of IS-IS PDU spoofing can be reduced by the use of <t>The possibility of IS-IS PDU spoofing can be reduced by the use of
authentication as described in [RFC1195] and [ISO10589], and especially authentication, as described in <xref target="RFC1195" format="default"/>
the use of cryptographic authentication as described in <xref and <xref target="ISO10589" format="default"/>, and especially by
target="RFC5304"/> and <xref target="RFC5310"/>.</t> the use of cryptographic authentication, as described in <xref target="RFC
5304" format="default"/> and <xref target="RFC5310" format="default"/>.</t>
</section> </section>
<section numbered="true" toc="default">
<section title="Manageability Considerations"> <name>Manageability Considerations</name>
<t>These extensions that have been designed, developed, and deployed for <t>These extensions that have been designed, developed, and deployed for
many years do not have any new impact on management and operation of the many years do not have any new impact on management and operation of the
IS-IS protocol via this standardization process.</t> IS-IS protocol via this standardization process.</t>
</section> </section>
<section anchor="Acknowledgements" title="Acknowledgements">
<t>For RFC 5306 the authors acknowledged contributions made by Jeff
Parker, Radia Perlman, Mark Schaefer, Naiming Shen, Nischal Sheth, Russ
White, and Rena Yang.</t>
<t>The authors of this updated version acknowledge the contribution of
Mike Shand, co-auther of RFC 5306.</t>
</section>
</middle> </middle>
<back> <back>
<references title="Normative References"> <references>
<name>Normative References</name>
<reference anchor="ISO10589"> <reference anchor="ISO10589">
<front> <front>
<title>Intermediate system to Intermediate system intra-domain <title>Information technology -- Telecommunications and information
exchange between systems -- Intermediate System to Intermediate System
intra-domain
routeing information exchange protocol for use in conjunction with routeing information exchange protocol for use in conjunction with
the protocol for providing the connectionless-mode Network Service the protocol for providing the connectionless-mode network service
(ISO 8473)</title> (ISO 8473)</title>
<seriesInfo name="ISO/IEC" value="10589:2002, Second Edition"/>
<author> <author>
<organization abbrev="ISO">International Organization for <organization abbrev="ISO">International Organization for
Standardization</organization> Standardization</organization>
</author> </author>
<date month="November" year="2002"/>
<date month="Nov" year="2002"/>
</front> </front>
<seriesInfo name="ISO/IEC" value="10589:2002, Second Edition"/>
</reference> </reference>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/referen
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.119 ce.RFC.1195.xml"/>
5.xml"?> <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/referen
ce.RFC.2119.xml"/>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.211 <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/referen
9.xml"?> ce.RFC.5303.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/referen
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.530 ce.RFC.5304.xml"/>
3.xml"?> <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/referen
ce.RFC.5310.xml"/>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.530 <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/referen
4.xml"?> ce.RFC.5880.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/referen
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.531 ce.RFC.8174.xml"/>
0.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.588
0.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.817
4.xml"?>
</references> </references>
<section numbered="true" toc="default">
<section title="Summary of Changes from RFC 5306"> <name>Summary of Changes from RFC 5306</name>
<t>This document extends RFC 5306 by introducing support for signalling <t>This document extends RFC 5306 by introducing support for signaling
the neighbors of a restarting router that a planned restart is about to the neighbors of a restarting router that a planned restart is about to
occur. This allows the neighbors to be aware of the state of the occur. This allows the neighbors to be aware of the state of the
restarting router so that appropriate action may be taken if other restarting router so that appropriate action may be taken if other
topology changes occur while the planned restart is in progress. Since topology changes occur while the planned restart is in progress. Since
the forwarding plane of the restarting router is maintained based upon the forwarding plane of the restarting router is maintained based upon
the pre-restart state of the network, additional topology changes the pre-restart state of the network, additional topology changes
introduce the possibility that traffic may be lost if paths via the introduce the possibility that traffic may be lost if paths via the
restarting router continue to be used while the restart is in restarting router continue to be used while the restart is in
progress.</t> progress.</t>
<t>In support of this new functionality, two new flags have been
<t>In support of this new functionality two new flags have been
introduced:</t> introduced:</t>
<t><figure> <dl newline="false" spacing="normal" indent="2">
<artwork><![CDATA[ PR - Restart is planned <dt>PR -</dt>
PA - Planned restart acknowledgement <dd>Restart is planned</dd>
]]></artwork> <dt>PA -</dt>
</figure></t> <dd>Planned restart acknowledgement</dd>
</dl>
<t>No changes to the post restart exchange between the restarting router <t>No changes to the post-restart exchange between the restarting router
and its neighbors have been introduced.</t> and its neighbors have been introduced.</t>
</section> </section>
<section anchor="Acknowledgements" numbered="false" toc="default">
<name>Acknowledgements</name>
<t>For RFC 5306, the authors acknowledged contributions made by
<contact fullname="Jeff Parker"/>,
<contact fullname="Radia Perlman"/>,
<contact fullname="Mark Schaefer"/>,
<contact fullname="Naiming Shen"/>,
<contact fullname="Nischal Sheth"/>,
<contact fullname="Russ White"/>, and
<contact fullname="Rena Yang"/>.</t>
<t>The authors of this updated document acknowledge the contribution of
<contact fullname="Mike Shand"/>, coauthor of RFC 5306.</t>
</section>
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</rfc> </rfc>
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