rfc8863xml2.original.xml   rfc8863.xml 
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<!DOCTYPE rfc SYSTEM "rfc2629.dtd" [ <!DOCTYPE rfc SYSTEM "rfc2629-xhtml.ent">
<!ENTITY RFC0822 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC
.2119.xml"> <rfc xmlns:xi="http://www.w3.org/2001/XInclude" ipr="trust200902"
<!ENTITY RFC0822 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC category="std" number="8863" docName="draft-ietf-ice-pac-06" obsoletes=""
.8174.xml"> updates="8445, 8838" submissionType="IETF" consensus="true" xml:lang="en" t
<!ENTITY RFC8445 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC ocInclude="true" sortRefs="false" version="3">
.8445.xml"> <!-- xml2rfc v2v3 conversion 2.45.2 -->
]>
<?rfc toc="yes" ?>
<?rfc compact="yes" ?>
<?rfc subcompact="yes" ?>
<?rfc sortrefs="no" ?>
<?rfc strict="yes" ?>
<rfc ipr="trust200902" category="std" docName="draft-ietf-ice-pac-06" obsoletes=
"" updates="8445" submissionType="IETF" xml:lang="en">
<front> <front>
<title abbrev="ICE PAC"> <title abbrev="ICE PAC">
Interactive Connectivity Establishment Patiently Awaiting Connectivity (IC E PAC) Interactive Connectivity Establishment Patiently Awaiting Connectivity (IC E PAC)
</title> </title>
<author initials="C.H." surname="Holmberg" fullname="Christer Holmberg"> <seriesInfo name="RFC" value="8863"/>
<author initials="C." surname="Holmberg" fullname="Christer Holmberg">
<organization>Ericsson</organization> <organization>Ericsson</organization>
<address> <address>
<postal> <postal>
<street>Hirsalantie 11</street> <street>Hirsalantie 11</street>
<code>02420</code> <code>02420</code>
<city>Jorvas</city> <city>Jorvas</city>
<country>Finland</country> <country>Finland</country>
</postal> </postal>
<email>christer.holmberg@ericsson.com</email> <email>christer.holmberg@ericsson.com</email>
</address> </address>
</author> </author>
<author initials="J." surname="Uberti" fullname="Justin Uberti"> <author initials="J." surname="Uberti" fullname="Justin Uberti">
<organization>Google</organization> <organization>Google</organization>
<address> <address>
<postal> <postal>
<street>747 6th St W</street> <street>747 6th St W</street>
<code>98033</code> <code>98033</code>
<city>Kirkland</city> <city>Kirkland</city>
<country>USA</country> <region>WA</region>
<country>United States of America</country>
</postal> </postal>
<email>justin@uberti.name</email> <email>justin@uberti.name</email>
</address> </address>
</author> </author>
<date month="January" year="2021"/>
<date year="2020"/>
<area>Transport</area>
<workgroup>ICE Working Group</workgroup>
<keyword>ICE</keyword> <keyword>ICE</keyword>
<keyword>PAC</keyword> <keyword>PAC</keyword>
<keyword>Candidate</keyword> <keyword>Candidate</keyword>
<abstract> <abstract>
<t> <t>
During the process of establishing peer-to-peer connectivity, During the process of establishing peer-to-peer connectivity,
ICE agents can encounter situations where they have Interactive Connectivity Establishment (ICE) agents can encounter
no candidate pairs to check, and, as a result, conclude that situations where they have no candidate pairs to check, and, as a
ICE processing has failed. However, because additional result, conclude that ICE processing has failed. However, because
candidate pairs can be discovered during ICE processing, additional candidate pairs can be discovered during ICE processing,
declaring failure at this point may be premature. This declaring failure at this point may be premature. This document
document discusses when these situations can occur and discusses when these situations can occur.
updates RFC8445 and RFC XXXX by requiring that an ICE agent
wait a minimum amount of time before declaring ICE failure,
even if there are no candidate pairs left to check.
</t> </t>
<t> <t>
[RFC EDITOR NOTE: Please replace RFC XXXX with the RFC number of This document updates RFCs 8445 and 8838 by requiring that
draft-ietf-ice-trickle once it has been published. Please also an ICE agent wait a minimum amount of time before declaring
indicate that this specification updates RFC XXXX.] ICE failure, even if there are no candidate pairs left to check.
</t> </t>
</abstract> </abstract>
</front> </front>
<middle> <middle>
<section title="Introduction" toc="default"> <section toc="default" numbered="true">
<name>Introduction</name>
<t> <t>
<xref target="RFC8445"></xref> describes a protocol, Interactive Connect ivity Establishment (ICE), <xref target="RFC8445" format="default"/> describes a protocol, Interact ive Connectivity Establishment (ICE),
for Network Address Translator (NAT) traversal for UDP-based communicati on. for Network Address Translator (NAT) traversal for UDP-based communicati on.
</t> </t>
<t> <t>
When using ICE, endpoints will typically exchange ICE candidates, When using ICE, endpoints will typically exchange ICE candidates,
form a list of candidate pairs, and then test each candidate pair to see form a list of candidate pairs, and then test each candidate pair to see
if connectivity can be established. If the test for a given pair fails, if connectivity can be established. If the test for a given pair fails,
it is marked accordingly, and if all pairs have failed, the overall it is marked accordingly, and if all pairs have failed, the overall
ICE process typically is considered to have failed. ICE process typically is considered to have failed.
</t> </t>
<t> <t>
During the process of connectivity checks, additional candidates may During the process of connectivity checks, additional candidates may
be created as a result of successful inbound checks from the remote be created as a result of successful inbound checks from the remote
peer. Such candidates are referred to as peer-reflexive candidates, peer. Such candidates are referred to as peer-reflexive candidates;
and once discovered, will be used to form new candidate pairs which will once discovered, these candidates will be used to form new candidate pai
rs, which will
be tested like any other. However, there is an inherent problem be tested like any other. However, there is an inherent problem
here; if, before learning about any peer-reflexive candidates, an here; if, before learning about any peer-reflexive candidates, an
endpoint runs out of candidate pairs to check, either because it has endpoint runs out of candidate pairs to check, either because it has
none, or it considers them all to have failed, it will prematurely none or it considers them all to have failed, it will prematurely
declare failure and terminate ICE processing. This problem can declare failure and terminate ICE processing. This problem can
occur in many common situations. occur in many common situations.
</t> </t>
<t> <t>
This specification updates <xref target="RFC8445"></xref>, by simply This specification updates <xref target="RFC8445" format="default"/>
and <xref target="RFC8838"/> by simply
requiring that an ICE agent wait a minimum amount of time before requiring that an ICE agent wait a minimum amount of time before
declaring ICE failure, even if there are no candidate pairs to check, declaring ICE failure, even if there are no candidate pairs to check
or if all candidate pairs have failed. This delay provides enough time or all candidate pairs have failed. This delay provides enough time
for the discovery of peer-reflexive candidates, which may eventually for the discovery of peer-reflexive candidates, which may eventually
lead to ICE processing completing successfully. lead to ICE processing completing successfully.
</t> </t>
</section> </section>
<section numbered="true" toc="default">
<section title="Conventions"> <name>Conventions</name>
<t> <t>The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>",
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>",
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "<bcp14>SHALL NOT</bcp14>", "<bcp14>SHOULD</bcp14>",
"MAY", and "OPTIONAL" in this document are to be interpreted as "<bcp14>SHOULD NOT</bcp14>",
described in BCP 14 <xref target="RFC2119"></xref> <xref target="RFC8174 "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
"></xref> "<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this document
when, and only when, they appear in all capitals, as shown here. are to be interpreted as described in BCP&nbsp;14
</t> <xref target="RFC2119"/> <xref target="RFC8174"/> when, and only
when, they appear in all capitals, as shown here.</t>
</section> </section>
<section numbered="true" toc="default">
<section title="Relevant Scenarios"> <name>Relevant Scenarios</name>
<t> <t>
As noted above, the core problem this specification attempts to As noted above, the core problem this specification attempts to
address is the situation where even after local gathering and remote address is the situation where even after local gathering and remote
candidate signaling has completed, the ICE agent immediately ends up candidate signaling have completed, the ICE agent immediately ends up
with no valid pairs and no candidate pairs left to check, resulting in with no valid pairs and no candidate pairs left to check, resulting in
a premature ICE failure. This failure is premature because not a premature ICE failure. This failure is premature because not
enough time has elapsed to allow for discovery of peer-reflexive enough time has elapsed to allow for discovery of peer-reflexive
candidates from inbound connectivity checks; if discovered, these candidates from inbound connectivity checks; if discovered, these
candidates are very likely to result in a valid pair. candidates are very likely to result in a valid pair.
</t> </t>
<t> <t>
In most ICE scenarios, the lengthy timeouts for connectivity check tra nsactions, In most ICE scenarios, the lengthy timeouts for connectivity check tra nsactions,
typically tens of seconds, will prevent this problem from occurring. H owever, there typically tens of seconds, will prevent this problem from occurring. H owever, there
are certain specific cases where this problem will frequently occur. are certain specific cases where this problem will frequently occur.
</t> </t>
<section title="No Candidates From Peer"> <section numbered="true" toc="default">
<t> <name>No Candidates from Peer</name>
Per RFC XXXX, an ICE agent can provide zero candidates of <t>
Per <xref target="RFC8838"/>, an ICE agent can provide zero candidat
es of
its own. If the agent somehow knows that the remote endpoint is its own. If the agent somehow knows that the remote endpoint is
directly reachable, gathering local candidates is unnecessary and directly reachable, gathering local candidates is unnecessary and
will only cause delays; the peer agent can discover the will only cause delays; the peer agent can discover the
appropriate local candidate via connectivity checks. appropriate local candidate via connectivity checks.
</t> </t>
<t> <t>
However, following the procedures from However, following the procedures from
<xref target="RFC8445"></xref> strictly will result in immediate <xref target="RFC8445" format="default"/> strictly will result in im mediate
ICE failure, since the checklist at the peer agent will be ICE failure, since the checklist at the peer agent will be
empty. empty.
</t> </t>
</section> </section>
<section title="All Candidates Discarded"> <section numbered="true" toc="default">
<t> <name>All Candidates Discarded</name>
<t>
Even if the ICE agent provides candidates, they may be discarded Even if the ICE agent provides candidates, they may be discarded
by the peer agent if it does not know what to do with them. by the peer agent if it does not know what to do with them.
For example, candidates may use an address family that the peer For example, candidates may use an address family that the peer
agent does not support, (e.g., a host candidate with an IPv6 agent does not support (e.g., a host candidate with an IPv6
address in a NAT64 scenario), or may not be usable for some other address in a NAT64 scenario) or that may not be usable for some othe
r
reason. reason.
</t> </t>
<t> <t>
In these scenarios, when the candidates are discarded, the In these scenarios, when the candidates are discarded, the
checklist at the peer agent will once again be empty, leading checklist at the peer agent will once again be empty, leading
to immediate ICE failure. to immediate ICE failure.
</t> </t>
</section> </section>
<section title="Immediate Candidate Pair Failure"> <section numbered="true" toc="default">
<t> <name>Immediate Candidate Pair Failure</name>
Section 7.2.5.2 of <xref target="RFC8445"></xref> describes several <t>
<xref target="RFC8445" sectionFormat="of" section="7.2.5.2"/>
describes several
situations in which a candidate pair will be considered to have situations in which a candidate pair will be considered to have
failed, well before the connectivity check transaction timeout. failed, well before the connectivity check transaction timeout.
</t> </t>
<t> <t>
As a result, even if the ICE agent provides usable candidates, As a result, even if the ICE agent provides usable candidates,
the pairs created by the peer agent may fail immediately when the pairs created by the peer agent may fail immediately when
checked, e.g., a check to a non-routable address that receives an checked, e.g., a check to a non-routable address that receives an
immediate ICMP error. immediate ICMP error.
</t> </t>
<t> <t>
In this situation, the checklist at the peer agent may contain In this situation, the checklist at the peer agent may contain
only failed pairs, resulting in immediate ICE failure. only failed pairs, resulting in immediate ICE failure.
</t> </t>
</section> </section>
</section> </section>
<section numbered="true" toc="default">
<section title="Update to RFC 8445"> <name>Update to RFC 8445</name>
<t> <t>
In order to avoid the problem raised by this document, the ICE agent In order to avoid the problem raised by this document, the ICE agent
needs to wait enough time to allow peer-reflexive candidates to be needs to wait enough time to allow peer-reflexive candidates to be
discovered. Accordingly, when a full ICE implementation begins its discovered. Accordingly, when a full ICE implementation begins its
ICE processing, as described in <xref target="RFC8445" />, Section ICE processing, as described in <xref target="RFC8445"
6.1, it MUST set a timer, henceforth known as the PAC timer, to sectionFormat="comma" section="6.1"/>, it <bcp14>MUST</bcp14> set a
ensure ICE will run for a minimum amount of time before determining timer, henceforth known as the "PAC timer" (Patiently Awaiting Connectiv
ity), to
ensure that ICE will run for a minimum amount of time before determining
failure. failure.
</t> </t>
<t> <t>
Specifically, the ICE agent will start its timer once it believes Specifically, the ICE agent will start its timer once it believes
ICE connectivity checks are starting. This occurs when the agent has ICE connectivity checks are starting. This occurs when the agent has
sent the values needed to perform connectivity checks sent the values needed to perform connectivity checks
(e.g., the Username Fragment and Password denoted in (e.g., the Username Fragment and Password denoted in
<xref target="RFC8445" />, Section 5.3) <xref target="RFC8445" sectionFormat="comma" section="5.3"/>)
and has received some indication that the remote side is and has received some indication that the remote side is
ready to start connectivity checks, typically via receipt of the values ready to start connectivity checks, typically via receipt of the values
mentioned above. Note that the agent will start the timer even if it mentioned above. Note that the agent will start the timer even if it
has not sent or received any ICE candidates. has not sent or received any ICE candidates.
</t> </t>
<t> <t>
The RECOMMENDED duration for the PAC timer is equal to the agent's The <bcp14>RECOMMENDED</bcp14> duration for the PAC timer is equal to th e agent's
connectivity check transaction timeout, including all retransmissions. connectivity check transaction timeout, including all retransmissions.
When using default values for RTO and Rc, this amounts to 39.5 seconds, When using default values for retransmission timeout (RTO) and Rc, this
as explained in <xref target="RFC5389" />, Section 7.2.1. amounts to 39.5 seconds,
as explained in <xref target="RFC5389" sectionFormat="comma"
section="7.2.1"/>.
This timeout value is chosen to roughly coincide with the maximum This timeout value is chosen to roughly coincide with the maximum
possible duration of ICE connectivity checks from the remote peer, possible duration of ICE connectivity checks from the remote peer,
which, if successful, could create peer-reflexive candidates. Because which, if successful, could create peer-reflexive candidates. Because
the ICE agent doesn't know the exact number of candidate pairs and pacin g the ICE agent doesn't know the exact number of candidate pairs and pacin g
interval in use by the remote side, this timeout value is simply a interval in use by the remote side, this timeout value is simply a
guess, albeit an educated one. Regardless, for this particular problem, guess, albeit an educated one. Regardless, for this particular problem,
the desired benefits will be realized as long as the agent waits the desired benefits will be realized as long as the agent waits
some reasonable amount of time, and, as usual, the application is in some reasonable amount of time, and, as usual, the application is in
the best position to determine what is reasonable for its scenario. the best position to determine what is reasonable for its scenario.
</t> </t>
<t> <t>
While the timer is still running, the ICE agent MUST NOT update a checkl ist state While the timer is still running, the ICE agent <bcp14>MUST NOT</bcp14> update a checklist state
from Running to Failed, even if there are no pairs left in the checklist to check. from Running to Failed, even if there are no pairs left in the checklist to check.
As a result, the ICE agent will not remove any data streams or set the s tate of the As a result, the ICE agent will not remove any data streams or set the s tate of the
ICE session to Failed as long as the timer is running. ICE session to Failed as long as the timer is running.
</t> </t>
<t> <t>
When the timer eventually elapses, the ICE agent MUST resume typical When the timer period eventually elapses, the ICE agent <bcp14>MUST</bcp 14> resume typical
ICE processing, including setting the state of any checklists to Failed if they ICE processing, including setting the state of any checklists to Failed if they
have no pairs left to check, and handling any consequences as indicated have no pairs left to check and handling any consequences as indicated
in <xref target="RFC8445" />, Section 8.1.2. Naturally, if there are no in <xref target="RFC8445" sectionFormat="comma" section="8.1.2"/>.
such checklists, no action is necessary. Naturally, if there are no such checklists, no action is necessary.
</t> </t>
<t> <t>
One consequence of this behavior is that in cases where ICE should fail, One consequence of this behavior is that in cases where ICE should fail,
e.g., where both sides provide candidates with unsupported address famil ies, e.g., where both sides provide candidates with unsupported address famil ies,
ICE will no longer fail immediately, and only fail when the ICE will no longer fail immediately -- it will only fail when the
PAC timer expires. However, because most ICE scenarios PAC timer expires. However, because most ICE scenarios
require an extended period of time to determine failure, the require an extended period of time to determine failure, the
fact that some specific scenarios no longer fail fast should have fact that some specific scenarios no longer fail quickly should have
minimal application impact, if any. minimal application impact, if any.
</t> </t>
<t> <t>
Note also that the PAC timer is potentially relevant to the ICE nominati on Note also that the PAC timer is potentially relevant to the ICE nominati on
procedure described in <xref target="RFC8445" />, Section 8.1.1. That procedure described in <xref target="RFC8445" sectionFormat="comma" sect ion="8.1.1"/>. That
specification does not define a minimum duration for ICE processing specification does not define a minimum duration for ICE processing
prior to nomination of a candidate pair, but in order to select the prior to nomination of a candidate pair, but in order to select the
best candidate pair, ICE needs to run for enough time in order to allow best candidate pair, ICE needs to run for enough time in order to allow
peer-reflexive candidates to be discovered and checked, as noted above. peer-reflexive candidates to be discovered and checked, as noted above.
Accordingly, the controlling ICE agent SHOULD wait a sufficient amount Accordingly, the controlling ICE agent <bcp14>SHOULD</bcp14> wait a suff
of time before nominating candidate pairs, and it MAY use the PAC timer icient amount
of time before nominating candidate pairs, and it <bcp14>MAY</bcp14> use
the PAC timer
to do so. As always, the controlling ICE agent retains to do so. As always, the controlling ICE agent retains
full discretion, and MAY decide, based on its own criteria, to nominate full discretion and <bcp14>MAY</bcp14> decide, based on its own criteria
pairs prior to the PAC timer elapsing. , to nominate
pairs prior to the PAC timer period elapsing.
</t> </t>
</section> </section>
<section numbered="true" toc="default">
<section title="Update to RFC XXXX"> <name>Update to RFC 8838</name>
<t>
[RFC EDITOR NOTE: Please replace RFC XXXX with the RFC number of
draft-ietf-ice-trickle once it has been published.]
</t>
<t> <t>
Trickle ICE <xref target="I-D.ietf-ice-trickle" /> Trickle ICE <xref target="RFC8838"/>
considers a similar problem, namely whether an ICE agent should allow considers a similar problem, namely whether an ICE agent should allow
a checklist to enter the Failed state if more candidates might a checklist to enter the Failed state if more candidates might
still be provided by the remote peer. The solution, specified in still be provided by the remote peer. The solution, specified in
<xref target="I-D.ietf-ice-trickle" />, Section 8, is to <xref target="RFC8838" sectionFormat="comma" section="8"/>, is to
wait until an end-of-candidates indication has been received wait until an end-of-candidates indication has been received
before determining ICE failure. before determining ICE failure.
</t> </t>
<t> <t>
However, for the same reasons described above, However, for the same reasons described above,
the ICE agent may discover peer-reflexive candidates after it has the ICE agent may discover peer-reflexive candidates after it has
received the end-of-candidates indication, and so the solution received the end-of-candidates indication, and so the solution
proposed by this document MUST still be used even when proposed by this document <bcp14>MUST</bcp14> still be used even when
the ICE agent is using Trickle ICE. the ICE agent is using Trickle ICE.
</t> </t>
<t> <t>
Note also that sending an end-of-candidates indication is only a Note also that sending an end-of-candidates indication is only a
SHOULD-strength requirement, which means that ICE agents will need <bcp14>SHOULD</bcp14>-strength requirement, which means that ICE agents will need
to implement a backup mechanism to decide when all candidates to implement a backup mechanism to decide when all candidates
have been received, typically a timer. Accordingly, ICE agents have been received, typically a timer. Accordingly, ICE agents
MAY use the PAC timer to also serve as an end-of-candidates fallback. <bcp14>MAY</bcp14> use the PAC timer to also serve as an end-of-candidat es fallback.
</t> </t>
</section> </section>
<section anchor="section.sec" numbered="true" toc="default">
<section anchor="section.sec" title="Security Considerations"> <name>Security Considerations</name>
<t> <t>
The security considerations for ICE are defined in <xref target="RFC8445 The security considerations for ICE are defined in <xref target="RFC8445
" pageno="false" format="default"/>. " format="default"/>.
This specification only recommends that ICE agents wait for a certain ti This specification only recommends that ICE agents wait for a certain
me of period before they declare period of time before they declare
ICE failure, and does not introduce new security considerations. ICE failure; it does not introduce new security considerations.
</t> </t>
</section> </section>
<section anchor="section.iana" numbered="true" toc="default">
<section anchor="section.iana" title="IANA considerations"> <name>IANA Considerations</name>
<t> <t>
This specification makes no requests to IANA. This document has no IANA actions.
</t> </t>
</section> </section>
</middle>
<back>
<references>
<name>Normative References</name>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2119.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5389.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8174.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8445.
xml"/>
<section anchor="sec-acks" title="Acknowledgements" toc="default"> <!-- draft-ietf-ice-trickle (RFC 8838) -->
<reference anchor="RFC8838" target="https://www.rfc-editor.org/info/rfc8838">
<front>
<title>Trickle ICE: Incremental Provisioning of Candidates for the
Interactive Connectivity Establishment (ICE) Protocol</title>
<author initials="E" surname="Ivov" fullname="Emil Ivov">
<organization />
</author>
<author initials="J" surname="Uberti" fullname="Justin Uberti">
<organization />
</author>
<author initials="P" surname="Saint-Andre" fullname="Peter Saint-Andre">
<organization />
</author>
<date month="January" year="2021" />
</front>
<seriesInfo name="RFC" value="8838" />
<seriesInfo name="DOI" value="10.17487/RFC8838"/>
</reference>
</references>
<section anchor="sec-acks" toc="default" numbered="false">
<name>Acknowledgements</name>
<t> <t>
Roman Shpount, Nils Ohlmeier and Peter Thatcher provided lots of useful input and <contact fullname="Roman Shpount"/>, <contact fullname="Nils Ohlmeier"/> , and <contact fullname="Peter Thatcher"/> provided lots of useful input and
comments. comments.
</t> </t>
</section> </section>
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.2119"?>
<?rfc include="reference.RFC.5389"?>
<?rfc include="reference.RFC.8174"?>
<?rfc include="reference.RFC.8445"?>
<?rfc include='reference.I-D.ietf-ice-trickle'?>
</references>
</back> </back>
</rfc> </rfc>
 End of changes. 54 change blocks. 
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