Internet DRAFT - draft-holmberg-ice-pac
draft-holmberg-ice-pac
ICE Working Group C. Holmberg
Internet-Draft Ericsson
Updates: 8445 (if approved) J. Uberti
Intended status: Standards Track Google
Expires: September 12, 2019 March 11, 2019
Interactive Connectivity Establishment Patiently Awaiting Connectivity
(ICE PAC)
draft-holmberg-ice-pac-01
Abstract
During the process of creating a peer-to-peer connection, ICE
implementations can encounter situations where they have no candidate
pairs to check, and, as a result, conclude that ICE processing has
failed. However, because additional candidate pairs can be
discovered during ICE processing, declaring failure at this point may
be premature. This document discusses when these situations can
occur and proposes a way to avoid premature failure.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 12, 2019.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
Holmberg & Uberti Expires September 12, 2019 [Page 1]
Internet-Draft ICE Premature March 2019
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Relevant Scenarios . . . . . . . . . . . . . . . . . . . . . 3
3.1. No Candidates From Peer . . . . . . . . . . . . . . . . . 3
3.2. All Candidates Discarded . . . . . . . . . . . . . . . . 3
3.3. Immediate Candidate Pair Failure . . . . . . . . . . . . 4
4. Update to RFC 8445 . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. IANA considerations . . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
8. Normative References . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
[RFC8445] describes a protocol, Interactive Connectivity
Establishment (ICE), for Network Address Translator (NAT) traversal
for UDP-based communication.
Typically, when using ICE, endpoints will exchange candidate
addresses, 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, it is marked accordingly, and if all
pairs have failed, the overall ICE process is considered to have
failed.
During the process of connectivity checks, additional candidates may
be created as a result of successful inbound checks from the remote
peer. Such candidates are referred to as peer-reflexive candidates,
and once discovered, will be used to form new candidate pairs which
will be tested like any other. However, there is an inherent race
condition here; if, before learning about any peer-reflexive
candidates, an endpoint runs out of candidate pairs to check, either
because it has none, or it considers them all to have failed, it will
prematurely declare failure and terminate ICE processing. This race
condition can occur in many common situations.
This specification updates [RFC8445], by simply requiring that an
endpoint wait a minimum amount of time before declaring ICE failure,
even if there are no candidate pairs to check, or if all candidate
pairs have failed. This delay provides enough time for the discovery
Holmberg & Uberti Expires September 12, 2019 [Page 2]
Internet-Draft ICE Premature March 2019
of peer-reflexive candidates, which may eventually lead to ICE
processing completing successfully.
2. Conventions
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 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Relevant Scenarios
As noted above, the core problem this specification attempts to
address is the situation where even after local gathering and remote
candidate signaling has completed, the ICE agent immediately ends up
with no valid pairs and no candidate pairs left to check, resulting
in a premature ICE failure. This failure is premature because not
enough time has elapsed to allow for discovery of peer-reflexive
candidates from inbound connectivity checks; if discovered, these
candidates are very likely to result in a valid pair.
In most ICE scenarios, the lengthy timeouts for connectivity checks,
typically tens of seconds, will prevent this problem for occuring.
However, there are certain specific cases where this problem will
frequently occur.
3.1. No Candidates From Peer
It is entirely legal for an ICE gent to provide zero candidates of
its own. If the agent somehow knows that the remote endpoint is
directly reachable, gathering local candidates is unnecessary and
will only cause delays; the remote endpoint can discover the
appropriate local candidate via connectivity checks.
However, following the procedures from [RFC8445] strictly will result
in immediate ICE failure, since the checklist at the remote endpoint
will be empty.
3.2. All Candidates Discarded
Even if the ICE agent provides candidates, they may be discarded by
the remote endpoint if it does not know what to do with them. For
example, candidates may use an address family that the remote
endpoint does not support, (e.g., a host candidate with an IPv6
address in a NAT64 scenario), or may not be usable for some other
reason (e.g., a candidate that contains a FQDN that fails to
resolve).
Holmberg & Uberti Expires September 12, 2019 [Page 3]
Internet-Draft ICE Premature March 2019
In these scenarios, when the candidates are discarded, the checklist
at the remote endpoint will once again be empty, leading to immediate
ICE failure.
3.3. Immediate Candidate Pair Failure
Section 7.2.5.2 of [RFC8445] describes several situations in which a
candidate pair will be considered to have failed, well before the
connectivity check timeout.
As a result, even if the ICE agent provides usable candidates, the
pairs created by the remote endpoint may fail immediately when
checked, e.g., a check to a nonroutable address that receives an
immediate ICMP error.
In this situation, the checklist at the remote endpoint may contain
only failed pairs, resulting in immediate ICE failure.
4. Update to RFC 8445
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
discovered. Accordingly, when full ICE implementations begin their
ICE processing, as described in [RFC8445], Section 6.1, the ICE agent
MUST set a timer, and its duration SHOULD be equal to the ICE agent's
connectivity check timeout.
This timeout value is chosen to roughly coincide with the maximum
possible duration of ICE connectivity checks from the remote peer,
which, if successful, could create peer-reflexive candidates.
Because the ICE agent doesn't know the exact number of candidate
pairs and pacing interval in use by the remote side, this timeout
value is simply a guess, albeit an educated one. Regardless, for
this particular problem, the desired benefits will be realized as
long as the ICE agent waits some reasonable amount of time.
While the timer is running, if a checklist has no pairs left to
check, i.e., there are no pairs that are not in the failed state, the
ICE agent MUST not conclude that ICE processing has failed, and MUST
wait for the timer to elapse before doing so.
One consequence of this behavior is that in cases where ICE should
fail, e.g., where both sides provide candidates with unresolvable
FQDNs ICE will no longer fail immediately, and only fail when the
aforementioned timer expires. However, because most ICE scenarios
require an extended period of time to determine failure, the fact
that some specific scenarios no longer fail fast should have minimal
application impact, if any.
Holmberg & Uberti Expires September 12, 2019 [Page 4]
Internet-Draft ICE Premature March 2019
5. Security Considerations
The security considerations for ICE are defined in [RFC8445]. This
specification only recommends ICE endpoints to wait for a certain
time of period before they declare ICE failure, and does not
introduce new security considerations.
6. IANA considerations
This specification makes no requests to IANA.
7. Acknowledgements
8. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc-
editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8445] Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive
Connectivity Establishment (ICE): A Protocol for Network
Address Translator (NAT) Traversal", RFC 8445,
DOI 10.17487/RFC8445, July 2018, <https://www.rfc-
editor.org/info/rfc8445>.
Authors' Addresses
Christer Holmberg
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: christer.holmberg@ericsson.com
Justin Uberti
Google
747 6th St W
Kirkland 98033
USA
Email: justin@uberti.name
Holmberg & Uberti Expires September 12, 2019 [Page 5]