<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE rfc SYSTEM "rfc2629-xhtml.ent">
<rfc number="8703" consensus="true" xmlns:xi="http://www.w3.org/2001/XInclude"
category="std" ipr="trust200902"
docName="draft-ietf-manet-dlep-lid-extension-06" obsoletes="" updates=""
submissionType="IETF" xml:lang="en" tocInclude="true" symRefs="true"
sortRefs="true" version="3">
<!-- xml2rfc v2v3 conversion 2.35.0 -->
<front>
<title abbrev="DLEP Link Identifier Extension">
Dynamic Link Exchange Protocol (DLEP) Link Identifier Extension</title>
<seriesInfo name="RFC" value="8703"/>
<author initials="R." surname="Taylor" fullname="Rick Taylor">
<organization>Airbus Defence & Space</organization>
<address>
<postal>
<extaddr>Quadrant House</extaddr>
<extaddr>Celtic Springs</extaddr>
<extaddr>Coedkernew</extaddr>
<city>Newport</city>
<code>NP10 8FZ</code>
<country>United Kingdom</country>
</postal>
<email>rick.taylor@airbus.com</email>
</address>
</author>
<author fullname="Stan Ratliff" initials="S." surname="Ratliff">
</author>
<date month="February" year="2020"/>
<area>Routing</area>
<workgroup>Mobile Ad hoc Networks Working Group</workgroup>
<keyword>DLEP</keyword>
<keyword>MANET</keyword>
<keyword>Link-Aware</keyword>
<keyword>Radio-Aware</keyword>
<abstract>
<t>The Dynamic Link Exchange Protocol (DLEP) is a protocol for modems to
advertise the status of wireless links between reachable destinations to
attached routers. The core specification of the protocol (RFC 8175)
assumes that every modem in the radio network has an attached DLEP
router and requires that the Media Access Control (MAC) address of the
DLEP interface on the attached router be used to identify the
destination in the network, for purposes of reporting the state and
quality of the link to that destination. </t>
<t>This document describes a DLEP extension that allows modems that do not
meet the strict requirement above to use DLEP to describe link
availability and quality to one or more destinations reachable beyond a
device on the Layer 2 domain. </t>
</abstract>
</front>
<middle>
<section anchor="introduction" toc="default" numbered="true">
<name>Introduction</name>
<t>The Dynamic Link Exchange Protocol (DLEP) is a
protocol for modems to advertise the status of wireless links between
reachable destinations to attached routers. The core specification of
the protocol <xref target="RFC8175"/> assumes that every modem in the radio network has an
attached DLEP router and requires that the MAC address of the DLEP
interface on the attached router be used to identify the destination in
the network, for purposes of reporting the state and quality of the link
to that destination. </t>
<t>This document describes a DLEP extension that allows modems that do not
meet the strict requirement above to use DLEP to describe link
availability and quality to one or more destinations reachable beyond a
device on the Layer 2 domain. </t>
<t>As with core DLEP <xref target="RFC8175"/>, a router can use this
knowledge to influence any routing or flow-control decisions regarding
traffic to this destination, understanding that such traffic flows via
Layer 3. </t>
<section anchor="terminology" toc="default" numbered="true">
<name>Terminology</name>
<dl newline="false" spacing="normal">
<dt>Local Layer 2 domain:</dt>
<dd>The Layer 2 domain that links the router and modem participants
of the current DLEP session. </dd>
<dt>Layer 3 DLEP Destination:</dt>
<dd>A DLEP Destination that is not directly addressable within the
local Layer 2 domain but is reachable via a node addressable within
the local Layer 2 domain. </dd>
<dt>Gateway Node:</dt>
<dd>The last device with a MAC address reachable in the local Layer
2 domain on the path from the DLEP router participant towards the
Layer 3 DLEP Destination. This device is commonly the DLEP peer
modem but could be another DLEP Destination in the Layer 2 domain.
</dd>
</dl>
</section>
<section anchor="applicability" toc="default" numbered="true">
<name>Applicability</name>
<t>This extension was designed primarily to address the following use
cases: </t>
<ol spacing="normal" type="1">
<li>A radio system that does not operate in Layer 2 bridge mode but
instead provides Layer 3 connectivity between destinations, often
using its own embedded Layer 3 routing function. </li>
<li>A point-to-multipoint tunnel system, such as a software-defined
wide-area network (SD-WAN)
deployment, where the tunnel provider acts as a modem that has
knowledge of the characteristics of the underlay network and
provides that information as availability and metrics between
tunnel endpoints in the overlay network. </li>
<li>A modem that provides connectivity to a remote wide-area network
via a wireless link, but the concept of a Layer 2 reachable remote
router does not apply. An example of such a modem would be an LTE
device or 802.11 station that provides variable connectivity to the
Internet. </li>
</ol>
<t>This list of use cases is not exhaustive, and this extension may
well be applicable to future, currently unforeseen, use cases. </t>
</section>
<section anchor="requirements" toc="default" numbered="true">
<name>Requirements Language</name>
<t>
The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>",
"<bcp14>REQUIRED</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 14 <xref target="RFC2119"/> <xref target="RFC8174"/>
when, and only when, they appear in all capitals, as shown here.
</t>
</section>
</section>
<section anchor="operation" toc="default" numbered="true">
<name>Operation</name>
<t>To refer to a Layer 3 DLEP Destination, the DLEP session participant
adds a Link Identifier Data Item (<xref target="lid_di"
format="default"></xref>) to the relevant
Destination Message and (as usual) includes
a MAC Address Data Item. When paired with a Link Identifier Data Item,
the MAC Address Data Item <bcp14>MUST</bcp14> contain the MAC address of the Gateway
Node. </t>
<t>As only modems are initially aware of Layer 3 DLEP Destinations, Link
Identifier Data Items referring to a new link <bcp14>MUST</bcp14> first appear in a
DLEP Destination Up Message from the modem to the router. Once a link
has been identified in this way, Link Identifier Data Items may be used
by either DLEP participant during the lifetime of a DLEP
session. Because of this, a router <bcp14>MUST NOT</bcp14> send a DLEP Destination
Announce Message containing a Link Identifier Data Item referring to a
link that has not been mentioned in a prior DLEP Destination Up
Message. If a modem receives such a message, it <bcp14>MUST</bcp14> terminate the
session by issuing a Session Termination Message containing a Status
Data Item with status code set to 131 ('Invalid Destination') and
transition to the Session Termination state. If a router receives a
Destination Up Message specifying a Link Identifier that has already
been used, the router <bcp14>MUST</bcp14> respond with a Destination Up Response
Message containing a Status Data Item with status code set to 130
('Invalid Data') and transition to the Session Termination state. </t>
<t>Because the MAC address associated with any DLEP Destination Message
containing a Link Identifier Data Item is not the Layer 2 address of the
final destination, all DLEP Destination Up Messages containing a Link
Identifier Data Item <bcp14>MUST</bcp14> contain Layer 3 information.
In the case of
modems that provide Layer 3 wide area network connectivity between
devices, this means one or more IPv4 or IPv6 Address Data Items
providing the Layer 3 address of the final destination.
When referring to
some upstream backbone network infrastructures, this means one or more
IPv4 or IPv6 Attached Subnet Data Items, for example: '0.0.0.0/0' or
'::/0'. This mechanism allows the DLEP peer router to understand the properties of
the link to those routes. The address or addresses in the IPv4 or IPv6
Address Data Items <bcp14>MUST</bcp14> be the addresses in use on the public side of
any Network Address Translation. </t>
<t>When the DLEP peer router wishes to route packets to the Layer 3 DLEP
Destination, the MAC address associated with the Gateway Node <bcp14>MUST</bcp14> be
used as the Layer 2 destination of the packet if it wishes to use the
modem network to forward the packet. </t>
<t>As routers populate their Routing Information Base with the IP
address of the next-hop router towards a destination, implementations
supporting this extension <bcp14>SHOULD</bcp14> announce at least one valid IPv4 or
IPv6 addresses of the Gateway Node; this removes the need for the router
to use an additional IP address resolution protocol before adding the
route to its Routing Information Base. </t>
<section anchor="identifier-restrictions" toc="default" numbered="true">
<name>Identifier Restrictions</name>
<t>A Link Identifier is, by default, 4 octets in length. If a modem
wishes to use a Link Identifier of a different length, it <bcp14>MUST</bcp14> be
announced using the Link
Identifier Length Data Item (<xref target="lid_len_di"
format="default"></xref>) contained in the DLEP Session
Initialization Response Message sent by the modem to the router.</t>
<t>During the lifetime of a DLEP session, the length of Link
Identifiers <bcp14>MUST</bcp14> remain constant, i.e., the Length field of the Link
Identifier Data Item <bcp14>MUST NOT</bcp14> differ between destinations. </t>
<t>The method for generating Link Identifiers is a modem
implementation matter and out of scope of this document. Routers must
not make any assumptions about the meaning of Link Identifiers or how
Link Identifiers are generated. </t>
<t>Within a single DLEP session, all Link Identifiers <bcp14>MUST</bcp14> be unique
per MAC address. This means that a Layer 3 DLEP Destination is
uniquely identified by the pair: {MAC Address,Link Identifier}. </t>
<t>Link Identifiers <bcp14>MUST NOT</bcp14> be reused, i.e., a {MAC Address,Link
Identifier} pair that has been used to refer to one Layer 3 DLEP
Destination <bcp14>MUST NOT</bcp14> be used again within the lifetime of a single
DLEP peer-to-peer session. </t>
</section>
<section anchor="negotiation" toc="default" numbered="true">
<name>Negotiation</name>
<t>To use this extension, as with all DLEP extensions, the extension
<bcp14>MUST</bcp14> be announced during DLEP session initialization. A router
advertises support by including the value 3 ('Link Identifiers') (<xref
target="tbd" format="default"></xref>), in the Extension Data Item
within the Session Initialization Message. A modem advertises support
by including the value 3 ('Link Identifiers') in the Extension Data Item
within the Session Initialization Response Message. If both DLEP peers
advertise support for this extension, then Link Identifier Data Items
can be included in DLEP Messages. </t>
<t>If a modem requires support for this extension in order to describe
destinations and the router does not advertise support, then the
modem <bcp14>MUST NOT</bcp14> include a Link Identifier Data Item in any DLEP
Message. However, the modem <bcp14>SHOULD NOT</bcp14> immediately terminate the DLEP
session; rather, it <bcp14>SHOULD</bcp14> use a combination of DLEP Session Messages
and DLEP Attached Subnet Data Items to provide general information.
</t>
</section>
</section>
<section anchor="new-data-items" toc="default" numbered="true">
<name>New Data Items</name>
<t>This extension introduces two new DLEP Data Items: 1) the Link
Identifier Length Data Item (<xref target="lid_len_di"
format="default"></xref>) used to announce the length of Link
Identifiers at session initialization and 2) the Link
Identifier Data Item (<xref target="lid_di" format="default"></xref>)
used to identify a Layer 3 link at or beyond a destination. </t>
<section anchor="lid_len_di" toc="default" numbered="true">
<name>Link Identifier Length Data Item</name>
<t>The Link Identifier Length Data Item is used by a DLEP modem
implementation to specify the length of Link Identifier Data Items. If
the router advertised support by including the value 3 ('Link
Identifiers') in the Extension Data Item inside the Session
Initialization Message, this Data Item <bcp14>MAY</bcp14> be used in the Session
Initialization Response Message if the specified length is not the
default value of 4 octets. If the router did not specify support by
including the value 3 ('Link Identifiers') in the Extension Data Item,
this Data Item <bcp14>MUST NOT</bcp14> be sent. </t>
<artwork name="" type="" align="left" alt=""><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data Item Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Identifier Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
<dl newline="false" spacing="normal">
<dt>Data Item Type:</dt>
<dd>
26 (see <xref target="tbd"></xref>) </dd>
<dt>Length:</dt>
<dd>2 </dd>
<dt>Link Identifier Length:</dt>
<dd>The length, in octets, of Link Identifiers used by the DLEP
modem for this session. </dd>
</dl>
<t>A Link Identifier Length Data Item that specifies a Link Identifier
Length of 4 octets (the default) is valid, even if it has no effect.
</t>
</section>
<section anchor="lid_di" toc="default" numbered="true">
<name>Link Identifier Data Item</name>
<t>The Link Identifier Data Item <bcp14>MAY</bcp14> be used wherever a MAC Address
Data Item is defined as usable in core DLEP <xref target="RFC8175"/>. </t>
<artwork name="" type="" align="left" alt=""><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data Item Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Identifier... :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
<dl newline="false" spacing="normal">
<dt>Data Item Type:</dt>
<dd>
27 (see <xref target="tbd"></xref>) </dd>
<dt>Length:</dt>
<dd>The length of the Data Item, by default 4, but may be different
if a Link Identifier Length Data Item (<xref
target="lid_len_di"></xref>) has been announced during session
initialization.</dd>
<dt>Link Identifier:</dt>
<dd>The unique identifier of the Layer 3 DLEP Destination. This Link
Identifier has no implicit meaning and is only used to discriminate
between multiple links. </dd>
</dl>
</section>
</section>
<section anchor="security-considerations" toc="default" numbered="true">
<name>Security Considerations</name>
<t>As an extension to core DLEP <xref target="RFC8175"/>, the security
considerations of that protocol apply to this extension. This extension
adds no additional security mechanisms or features. </t>
<t>None of the features introduced by this extension require extra
security considerations by an implementation. </t>
</section>
<section anchor="tbd" toc="default" numbered="true">
<name>IANA Considerations</name>
<t>IANA has assigned the following value to the "Extension Type Values" registry
within the "Dynamic Link Exchange Protocol (DLEP) Parameters"
registry. This new value is
in the range with the "Specification Required" <xref target="RFC8126"/>
policy.
</t>
<table anchor="iana1" align="left">
<name>Addition to the Extension Type Values Registry</name>
<thead>
<tr>
<th>Code</th>
<th>Description</th>
</tr>
</thead>
<tbody>
<tr>
<td>3</td>
<td>Link Identifiers</td>
</tr>
</tbody>
</table>
<t>IANA has assigned two new values to the "Data Item Type Values" registry
within the "Dynamic Link Exchange Protocol (DLEP) Parameters" registry. These
new values are in the range with the "Specification Required" <xref
target="RFC8126"/> policy.
</t>
<table anchor="iana2" align="left">
<name>Additions to the Data Item Type Values Registry</name>
<thead>
<tr>
<th>Type Code</th>
<th>Description</th>
</tr>
</thead>
<tbody>
<tr>
<td>26</td>
<td>Link Identifier Length</td>
</tr>
<tr>
<td>27</td>
<td>Link Identifier</td>
</tr>
</tbody>
</table>
</section>
</middle>
<back>
<references>
<name>References</name>
<references>
<name>Normative References</name>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8175.xml"/>
</references>
<references>
<name>Informative References</name>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8126.xml"/>
</references>
</references>
</back>
</rfc>