Path MTU Discovery Using Session Traversal Utilities for NAT (STUN)
draft-ietf-tram-stun-pmtud-02
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| Last updated | 2016-07-25 | ||
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draft-ietf-tram-stun-pmtud-02
TRAM M. Petit-Huguenin
Internet-Draft Impedance Mismatch
Intended status: Standards Track G. Salgueiro
Expires: January 26, 2017 Cisco
July 25, 2016
Path MTU Discovery Using Session Traversal Utilities for NAT (STUN)
draft-ietf-tram-stun-pmtud-02
Abstract
This document describes a Session Traversal Utilities for NAT (STUN)
usage for Path MTU Discovery (PMTUD) between a client and a server.
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 January 26, 2017.
Copyright Notice
Copyright (c) 2016 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
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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Probing Mechanisms . . . . . . . . . . . . . . . . . . . . . 3
4. Simple Probing Mechanism . . . . . . . . . . . . . . . . . . 4
4.1. Sending a Probe Request . . . . . . . . . . . . . . . . . 4
4.2. Receiving a Probe Request . . . . . . . . . . . . . . . . 4
4.3. Receiving a Probe Response . . . . . . . . . . . . . . . 5
5. Complete Probing Mechanism . . . . . . . . . . . . . . . . . 5
5.1. Sending the Probe Indications and Report Request . . . . 5
5.2. Receiving an ICMP packet . . . . . . . . . . . . . . . . 5
5.3. Receiving a Probe Indication and Report Request . . . . . 5
5.4. Receiving a Report Response . . . . . . . . . . . . . . . 6
5.5. Using Checksum as Packet Identifiers . . . . . . . . . . 6
5.6. Using Sequential Numbers as Packet Identifiers . . . . . 6
6. Probe Support Discovery Mechanisms . . . . . . . . . . . . . 7
6.1. Implicit Mechanism . . . . . . . . . . . . . . . . . . . 7
6.2. Probe Support Discovery with TURN . . . . . . . . . . . . 7
6.3. Probe Support Discovery with ICE . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8.1. New STUN Methods . . . . . . . . . . . . . . . . . . . . 8
8.2. New STUN Attributes . . . . . . . . . . . . . . . . . . . 8
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
10.1. Normative References . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . 9
Appendix A. Release Notes . . . . . . . . . . . . . . . . . . . 9
A.1. Modifications between draft-ietf-tram-stun-pmtud-02 and
draft-ietf-tram-stun-pmtud-01 . . . . . . . . . . . . . . 10
A.2. Modifications between draft-ietf-tram-stun-pmtud-01 and
draft-ietf-tram-stun-pmtud-00 . . . . . . . . . . . . . . 10
A.3. Modifications between draft-ietf-tram-stun-pmtud-00 and
draft-petithuguenin-tram-stun-pmtud-01 . . . . . . . . . 10
A.4. Modifications between draft-petithuguenin-tram-stun-
pmtud-01 and draft-petithuguenin-tram-stun-pmtud-00 . . . 10
A.5. Modifications between draft-petithuguenin-tram-stun-
pmtud-00 and draft-petithuguenin-behave-stun-pmtud-03 . . 10
A.6. Modifications between draft-petithuguenin-behave-stun-
pmtud-03 and draft-petithuguenin-behave-stun-pmtud-02 . . 10
A.7. Modifications between draft-petithuguenin-behave-stun-
pmtud-02 and draft-petithuguenin-behave-stun-pmtud-01 . . 10
A.8. Modifications between draft-petithuguenin-behave-stun-
pmtud-01 and draft-petithuguenin-behave-stun-pmtud-00 . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
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1. Introduction
The Packetization Layer Path MTU Discovery specification [RFC4821]
describes a method to discover the path MTU but does not describe a
practical protocol to do so with UDP.
This document only describes how probing mechanisms are implemented
with Session Traversal Utilities for NAT (STUN). The algorithm to
find the path MTU is described in [RFC4821].
The STUN usage defined in this document for Path MTU Discovery
(PMTUD) between a client and a server simplifies troubleshooting and
has multiple applications across a wide variety of technologies.
Additional network characteristics like the network path (using the
STUN Traceroute mechanism described in
[I-D.martinsen-tram-stuntrace]) and bandwidth availability (using the
mechanism described in [I-D.martinsen-tram-turnbandwidthprobe]) can
be discovered using complementary techniques.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. When these
words are not in ALL CAPS (such as "must" or "Must"), they have their
usual English meanings, and are not to be interpreted as RFC 2119 key
words.
3. Probing Mechanisms
A client MUST NOT send a probe if it does not have knowledge that the
server supports this specification. This is done by an external
mechanism specific to each UDP protocol. Section 6 describes some of
this mechanisms.
The probe mechanism is used to discover the path MTU in one direction
only, from the client to the server.
Two probing mechanisms are described, a simple probing mechanism and
a more complete mechanism that can converge quicker.
The simple probing mechanism is implemented by sending a Probe
Request with a PADDING [RFC5780] attribute and the DF bit set over
UDP. A router on the path to the server can reject this request with
an ICMP message or drop it. The client SHOULD cease retransmissions
after 3 missing responses.
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The complete probing mechanism is implemented by sending one or more
Probe Indication with a PADDING attribute and the DF bit set over UDP
then a Report Request to the same server. A router on the path to
the server can reject this indication with an ICMP message or drop
it. The server keeps a time ordered list of identifiers of all
packets received (including retransmitted packets) and sends this
list back to the client in the Report Response. The client analyzes
this list to find which packets were not received. Because UDP
packets does not contain an identifier, the complete probing
mechanism needs a way to identify each packet received. While there
are other possible packet identification schemes, this document
describes two different ways to identify a specific packet.
In the first packet identifier mechanism, the server computes a
checksum over each packet received and sends back to the sender the
ordered list of checksums. The client compares this list to its own
list of checksums.
In the second packet identifier mechanism, the client adds a
sequential number in front of each UDP packet sent. The server sends
back the ordered list of sequential numbers received that the client
compares to its own list
4. Simple Probing Mechanism
4.1. Sending a Probe Request
A client forms a Probe Request by following the rules in Section 7.1
of [RFC5389]. No authentication method is used. The client adds a
PADDING [RFC5780] attribute with a length that, when added to the IP
and UDP headers and the other STUN components, is equal to the
Selected Probe Size, as defined in [RFC4821] section 7.3. The client
MUST add the FINGERPRINT attribute.
Then the client sends the Probe Request to the server over UDP with
the DF bit set. The client SHOULD stop retransmitting after 3
missing responses.
4.2. Receiving a Probe Request
A server receiving a Probe Request MUST process it as specified in
[RFC5389]. The server MUST NOT challenge the client.
The server then creates a Probe Response. The server MUST add the
FINGERPRINT attribute. The server then sends the response to the
client.
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4.3. Receiving a Probe Response
A client receiving a Probe Response MUST process it as specified in
[RFC5389]. If a response is received this is interpreted as a Probe
Success as defined in [RFC4821] section 7.6.1. If an ICMP packet
"Fragmentation needed" is received then this is interpreted as a
Probe Failure as defined in [RFC4821] section 7.6.2. If the Probe
transactions fails in timeout, then this is interpreted as a Probe
Inconclusive as defined in [RFC4821] section 7.6.4.
5. Complete Probing Mechanism
5.1. Sending the Probe Indications and Report Request
A client forms a Probe Indication by following the rules in [RFC5389]
section 7.1. The client adds to the Probe Indication a PADDING
attribute with a size that, when added to the IP and UDP headers and
the other STUN components, is equal to the Selected Probe Size, as
defined in [RFC4821] section 7.3. The client MUST add the
FINGERPRINT attribute.
Then the client sends the Probe Indication to the server over UDP
with the DF bit set.
Then the client forms a Report Request by following the rules in
[RFC5389] section 7.1. No authentication method is used. The client
MUST add the FINGERPRINT attribute.
Then the client waits half the RTO if it is known or 50 milliseconds
after sending the Probe Indication and sends the Report Request to
the server over UDP.
5.2. Receiving an ICMP packet
If an ICMP packet "Fragmentation needed" is received then this is
interpreted as a Probe Failure as defined in [RFC4821] section 7.5.
5.3. Receiving a Probe Indication and Report Request
A server supporting this specification and knowing that the client
also supports it will keep the identifiers of all packets received in
a list ordered by receiving time. The same identifier can appear
multiple times in the list because of retransmission. The maximum
size of this list is calculated so that when the list is added to the
Report Response, the total size of the packet does not exceed the
unknown path MTU as defined in [RFC5389] section 7.1. Older
identifiers are removed when new identifiers are added to a list
already full.
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A server receiving a Report Request MUST process it as specified in
[RFC5389]. The server MUST NOT challenge the client.
The server creates a Report Response and adds an IDENTIFIERS
attribute that contains the list of all identifiers received so far.
The server MUST add the FINGERPRINT attribute. The server then sends
the response to the client.
5.4. Receiving a Report Response
A client receiving a Report Response processes it as specified in
[RFC5389]. If the response IDENTIFIERS attribute contains the
identifier of the Probe Indication, then this is interpreted as a
Probe Success for this probe as defined in [RFC4821] Section 7.5. If
the Probe Indication identifier cannot be found in the Report
Response, this is interpreted as a Probe Failure as defined in
[RFC4821] Section 7.5. If the Probe Indication identifier cannot be
found in the Report Response but other packets identifier sent before
or after the Probe Indication cannot also be found, this is
interpreted as a Probe Inconclusive as defined in [RFC4821]
Section 7.5. If the Report Transaction fails in timeout, this is
interpreted as a Full-Stop Timeout as defined in [RFC4821] Section 3.
5.5. Using Checksum as Packet Identifiers
When using checksum as packet identifiers, the client calculate the
checksum for each packet sent over UDP and keep this checksum in an
ordered list. The server does the same thing and send back this list
in the Report Response.
It could have been possible to use the checksum generated in the UDP
checksum for this, but this value is generally not accessible to
applications. Also sometimes the checksum is not calculated or off-
loaded to the network card.
5.6. Using Sequential Numbers as Packet Identifiers
When using sequential numbers, a small header similar to the TURN
ChannelData header is added in front of all non-STUN packets. The
sequential number is incremented for each packet sent. The server
collects the sequence number of the packets sent.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Channel Number | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
/ Application Data /
/ /
| |
| +-------------------------------+
| |
+-------------------------------+
The Channel Number is always 0xFFFF.
6. Probe Support Discovery Mechanisms
6.1. Implicit Mechanism
An endpoint acting as a client for the STUN usage described in this
specification MUST also act as a server for this STUN usage. This
means that a server receiving a probe can assumes that it can acts as
a client to discover the path MTU to the IP address and port from
which it received the probe.
6.2. Probe Support Discovery with TURN
A TURN client supporting this STUN usage will add a PMTUD-SUPPORTED
attribute to the Allocate Request sent to the TURN server. The TURN
server can immediately start to send probes to the TURN client on
reception of an Allocation Request with a PMTUD-SUPPORTED attribute.
The TURN client will then use the Implicit Mechanism described above
to send probes.
6.3. Probe Support Discovery with ICE
An ICE [RFC5245] client supporting this STUN usage will add a PMTUD-
SUPPORTED attribute to the Binding Request sent during a connectivity
check. The ICE server can immediately start to send probes to the
ICE client on reception of a Binding Request with a PMTUD-SUPPORTED
attributed. Local candidates receiving Binding Request with the
PMTUD-SUPPORTED flag must not start PMTUD with the remote candidate
if already done so. The ICE client will then use the Implicit
Mechanism described above to send probes.
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7. Security Considerations
The PMTUD mechanism described in this document does not introduce any
specific security considerations beyond those described in [RFC4821].
The attack described in [RFC4821] applies equally to the mechanism
described in this document.
8. IANA Considerations
This specification defines two new STUN method and two new STUN
attributes. IANA added these new protocol elements to the "STUN
Parameters Registry" created by [RFC5389].
8.1. New STUN Methods
This section lists the codepoints for the new STUN methods defined in
this specification. See Sections Section 4 and Section 5 for the
semantics of these new methods.
0xXXX : Probe
0xXXX : Report
8.2. New STUN Attributes
This document defines the IDENTIFIERS STUN attribute, described in
Section 5. IANA has allocated the comprehension-required codepoint
0xXXXX for this attribute.
This document also defines the PMTUD-SUPPORTED STUN attribute,
described in Section 6. IANA has allocated the comprehension-
optional codepoint 0xXXXX for this attribute.
9. Acknowledgements
Thanks to Eilon Yardeni, Geir Sandbakken and Paal-Erik Martinsen for
their review comments, suggestions and questions that helped to
improve this document.
Special thanks to Dan Wing, who supported this document since its
first publication back in 2008.
10. References
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10.1. 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,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU
Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007,
<http://www.rfc-editor.org/info/rfc4821>.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245,
DOI 10.17487/RFC5245, April 2010,
<http://www.rfc-editor.org/info/rfc5245>.
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389,
DOI 10.17487/RFC5389, October 2008,
<http://www.rfc-editor.org/info/rfc5389>.
10.2. Informative References
[I-D.martinsen-tram-stuntrace]
Martinsen, P. and D. Wing, "STUN Traceroute", draft-
martinsen-tram-stuntrace-01 (work in progress), June 2015.
[I-D.martinsen-tram-turnbandwidthprobe]
Martinsen, P., Andersen, T., Salgueiro, G., and M. Petit-
Huguenin, "Traversal Using Relays around NAT (TURN)
Bandwidth Probe", draft-martinsen-tram-
turnbandwidthprobe-00 (work in progress), May 2015.
[RFC5780] MacDonald, D. and B. Lowekamp, "NAT Behavior Discovery
Using Session Traversal Utilities for NAT (STUN)",
RFC 5780, DOI 10.17487/RFC5780, May 2010,
<http://www.rfc-editor.org/info/rfc5780>.
Appendix A. Release Notes
This section must be removed before publication as an RFC.
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A.1. Modifications between draft-ietf-tram-stun-pmtud-02 and draft-
ietf-tram-stun-pmtud-01
o Cleaned up references.
A.2. Modifications between draft-ietf-tram-stun-pmtud-01 and draft-
ietf-tram-stun-pmtud-00
o Added Security Considerations Section.
o Added IANA Considerations Section.
A.3. Modifications between draft-ietf-tram-stun-pmtud-00 and draft-
petithuguenin-tram-stun-pmtud-01
o Adopted by WG - Text unchanged.
A.4. Modifications between draft-petithuguenin-tram-stun-pmtud-01 and
draft-petithuguenin-tram-stun-pmtud-00
o Moved some Introduction text to the Probing Mechanism section.
o Added cross-reference to the other two STUN troubleshooting
mechanism drafts.
o Updated references.
o Added Gonzalo Salgueiro as co-author.
A.5. Modifications between draft-petithuguenin-tram-stun-pmtud-00 and
draft-petithuguenin-behave-stun-pmtud-03
o General refresh for republication.
A.6. Modifications between draft-petithuguenin-behave-stun-pmtud-03 and
draft-petithuguenin-behave-stun-pmtud-02
o Changed author address.
o Changed the IPR to trust200902.
A.7. Modifications between draft-petithuguenin-behave-stun-pmtud-02 and
draft-petithuguenin-behave-stun-pmtud-01
o Replaced the transactions identifiers by packet identifiers
o Defined checksum and sequential numbers as possible packet
identifiers.
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o Updated the reference to RFC 5389
o The FINGERPRINT attribute is now mandatory.
o Changed the delay between Probe indication and Report request to
be RTO/2 or 50 milliseconds.
o Added ICMP packet processing.
o Added Full-Stop Timeout detection.
o Stated that Binding request with PMTUD-SUPPORTED does not start
the PMTUD process if already started.
A.8. Modifications between draft-petithuguenin-behave-stun-pmtud-01 and
draft-petithuguenin-behave-stun-pmtud-00
o Removed the use of modified STUN transaction but shorten the
retransmission for the simple probing mechanism.
o Added a complete probing mechanism.
o Removed the PADDING-RECEIVED attribute.
o Added release notes.
Authors' Addresses
Marc Petit-Huguenin
Impedance Mismatch
Email: marc@petit-huguenin.org
Gonzalo Salgueiro
Cisco Systems, Inc.
7200-12 Kit Creek Road
Research Triangle Park, NC 27709
United States
Email: gsalguei@cisco.com
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