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Versions: (draft-petithuguenin-tram-stun-pmtud) 00 01 02 03 04 05

TRAM                                                   M. Petit-Huguenin
Internet-Draft                                        Impedance Mismatch
Intended status: Standards Track                            G. Salgueiro
Expires: August 24, 2017                                           Cisco
                                                       February 20, 2017


  Path MTU Discovery Using Session Traversal Utilities for NAT (STUN)
                     draft-ietf-tram-stun-pmtud-05

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 August 24, 2017.

Copyright Notice

   Copyright (c) 2017 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.  Overview of Operations  . . . . . . . . . . . . . . . . . . .   3
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Probing Mechanisms  . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Simple Probing Mechanism  . . . . . . . . . . . . . . . .   5
       4.1.1.  Sending a Probe Request . . . . . . . . . . . . . . .   5
       4.1.2.  Receiving a Probe Request . . . . . . . . . . . . . .   6
       4.1.3.  Receiving a Probe Response  . . . . . . . . . . . . .   6
     4.2.  Complete Probing Mechanism  . . . . . . . . . . . . . . .   6
       4.2.1.  Sending the Probe Indications and Report Request  . .   7
       4.2.2.  Receiving an ICMP Packet  . . . . . . . . . . . . . .   7
       4.2.3.  Receiving a Probe Indication and Report Request . . .   8
       4.2.4.  Receiving a Report Response . . . . . . . . . . . . .   8
       4.2.5.  Using Checksums as Packet Identifiers . . . . . . . .   9
       4.2.6.  Using Sequence Numbers as Packet Identifiers  . . . .   9
   5.  Probe Support Signaling Mechanisms  . . . . . . . . . . . . .  10
     5.1.  Explicit Probe Support Signaling Mechanism  . . . . . . .  10
     5.2.  Implicit Probe Support Signaling Mechanism  . . . . . . .  11
   6.  STUN Attributes . . . . . . . . . . . . . . . . . . . . . . .  11
     6.1.  IDENTIFIERS . . . . . . . . . . . . . . . . . . . . . . .  11
     6.2.  PMTUD-SUPPORTED . . . . . . . . . . . . . . . . . . . . .  11
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
     8.1.  New STUN Methods  . . . . . . . . . . . . . . . . . . . .  12
     8.2.  New STUN Attributes . . . . . . . . . . . . . . . . . . .  12
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Appendix A.  Release Notes  . . . . . . . . . . . . . . . . . . .  13
     A.1.  Modifications between draft-ietf-tram-stun-pmtud-04 and
           draft-ietf-tram-stun-pmtud-03 . . . . . . . . . . . . . .  13
     A.2.  Modifications between draft-ietf-tram-stun-pmtud-03 and
           draft-ietf-tram-stun-pmtud-02 . . . . . . . . . . . . . .  13
     A.3.  Modifications between draft-ietf-tram-stun-pmtud-02 and
           draft-ietf-tram-stun-pmtud-01 . . . . . . . . . . . . . .  14
     A.4.  Modifications between draft-ietf-tram-stun-pmtud-01 and
           draft-ietf-tram-stun-pmtud-00 . . . . . . . . . . . . . .  14
     A.5.  Modifications between draft-ietf-tram-stun-pmtud-00 and
           draft-petithuguenin-tram-stun-pmtud-01  . . . . . . . . .  14
     A.6.  Modifications between draft-petithuguenin-tram-stun-
           pmtud-01 and draft-petithuguenin-tram-stun-pmtud-00 . . .  15
     A.7.  Modifications between draft-petithuguenin-tram-stun-
           pmtud-00 and draft-petithuguenin-behave-stun-pmtud-03 . .  15
     A.8.  Modifications between draft-petithuguenin-behave-stun-
           pmtud-03 and draft-petithuguenin-behave-stun-pmtud-02 . .  15
     A.9.  Modifications between draft-petithuguenin-behave-stun-



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           pmtud-02 and draft-petithuguenin-behave-stun-pmtud-01 . .  15
     A.10. Modifications between draft-petithuguenin-behave-stun-
           pmtud-01 and draft-petithuguenin-behave-stun-pmtud-00 . .  16
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Introduction

   The Packetization Layer Path MTU Discovery (PMTUD) specification
   [RFC4821] describes a method to discover the Path MTU but does not
   describe a practical protocol to do so with UDP.

   Not all UDP-based protocols implement the Path MTU discovery
   mechanism described in [RFC4821].  These protocols can make use of
   the probing mechanisms described in this document instead of
   designing their own adhoc extension.  These probing mechanisms are
   implemented with Session Traversal Utilities for NAT (STUN), but
   their usage is not limited to STUN-based protocols.

   The STUN usage defined in this document for Path MTU Discovery
   (PMTUD) between a client and a server permits proper operations of
   UDP-based applications in the network.  It also simplifies
   troubleshooting and has multiple other applications across a wide
   variety of technologies.

   Complementary techniques can be used to discover additional network
   characteristics, such as 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]).

2.  Overview of Operations

   This section is meant to be informative only.  It is not intended as
   a replacement for [RFC4821].

   A UDP endpoint that uses this specification to discover the Path MTU
   over UDP and knows that the endpoint it is communicating with also
   supports this specification can choose to use either the Simple
   Probing mechanism (as described in Section 4.1) or the Complete
   Probing mechanism (as described in Section 4.2).  The selection of
   which Probing Mechanism to use is dependent on performance and
   security and complexity trade-offs.

   If the Simple Probing mechanism is chosen, then the Client initiates
   Probe transactions, as shown in Figure 1, which increase in size
   until transactions timeout, indicating that the Path MTU has been
   exceeded.  It then uses that information to update the Path MTU.



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                          Client           Server
                            |                 |
                            | Probe Request   |
                            |---------------->|
                            |                 |
                            |  Probe Response |
                            |<----------------|
                            |                 |

                     Figure 1: Simple Probing Example

   If the Complete Probing mechanism (as described in Section 4.2) is
   chosen, then the Client sends Probe Indications of various sizes
   interleaved with UDP packets sent by the UDP protocol.  The Client
   then sends a Report Request for the ordered list of identifiers for
   the UDP packets and Probe Indications received by the Server.  The
   Client then compares the list returned in the Report Response with
   its own list of identifiers for the UDP packets and Probe Indications
   it sent.  The Client then uses that comparison to find which Probe
   Indications were dropped by the network as a result of their size.
   It then uses that information to update the Path MTU.

                        Client              Server
                           | UDP Packet        |
                           |------------------>|
                           |                   |
                           | UDP Packet        |
                           |------------------>|
                           |                   |
                           | Probe Indication  |
                           |------------------>|
                           |                   |
                           | UDP Packet        |
                           |------------------>|
                           |                   |
                           | Probe Indication  |
                           |------------------>|
                           |                   |
                           | Report Request    |
                           |------------------>|
                           |   Report Response |
                           |<------------------|
                           |                   |

                    Figure 2: Complete Probing Example






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3.  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.

4.  Probing Mechanisms

   The Probing 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 and find an
   appropriate PMTU in the presence of congestion.  Additionally, the
   Simple Probing mechanism does not require authentication, whereas the
   complete mechanism does.

   Implementations supporting this specification MUST implement the
   server side of both the Simple Probing mechanism (Section 4.1) and
   the Complete Probing mechanism (Section 4.2).

   Implementations supporting this specification MUST implement the
   client side of the Complete Probing mechanism.  They MAY implement
   the client side of the Simple Probing mechanism.

4.1.  Simple Probing Mechanism

   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.

4.1.1.  Sending a Probe Request

   A client forms a Probe Request by using the Probe Method and
   following the rules in Section 7.1 of [RFC5389].

   The Probe transaction MUST be authenticated if the Simple Probing
   mechanism is used in conjunction with the Implicit Probing Support
   mechanism described in Section 5.2 If not, the Probe transaction MAY
   be authenticated.

   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]



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   Section 7.3.  The client MUST add the FINGERPRINT attribute so the
   STUN messages are disambiguated from the other protocol packets.

   Then the client sends the Probe Request to the server over UDP with
   the DF bit set.  For the purpose of this transaction, the Rc
   parameter specified in Section 7.2.1 of [RFC5389] is set to 3.  The
   initial value for RTO stays at 500 ms.

   A client MUST NOT send a probe if it does not have knowledge that the
   server supports this specification.  This is done either by external
   signalling or by a mechanism specific to the UDP protocol to which
   PMTUD capabilities are added or by one of the mechanisms specified in
   Section 5.

4.1.2.  Receiving a Probe Request

   A server receiving a Probe Request MUST process it as specified in
   [RFC5389].

   The server then creates a Probe Response.  The server MUST add the
   FINGERPRINT attribute so the STUN messages are disambiguated from the
   other protocol packets.  The server then sends the response to the
   client.

4.1.3.  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
   transaction times out, then this is interpreted as a Probe
   Inconclusive, as defined in [RFC4821] Section 7.6.4.

4.2.  Complete Probing Mechanism

   The Complete Probing mechanism is implemented by sending one or more
   Probe Indications with a PADDING attribute and the DF bit set over
   UDP followed by 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 chronologically ordered list of
   identifiers for 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 do not contain an identifier, the
   Complete Probing mechanism needs a way to identify each packet
   received.




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   Some protocols may already have a way of identifying each individual
   UDP packet, in which case these identifiers SHOULD be used in the
   IDENTIFIERS attribute of the Report Response.  While there are other
   possible packet identification schemes, this document describes two
   different ways to identify a specific packet.

   In the first packet identification mechanism, the server computes a
   checksum over each packet received and sends back to the sender the
   list of checksums ordered chronologically.  The client compares this
   list to its own list of checksums.

   In the second packet identification mechanism, the client prepends
   the UDP data with a header that provides a sequence number.  The
   server sends back the chronologically ordered list of sequence
   numbers received that the client then compares with its own list.

4.2.1.  Sending the Probe Indications and Report Request

   A client forms a Probe Indication by using the Probe Method and
   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.  If the
   authentication mechanism permits it, then the Indication MUST be
   authenticated.  The client MUST add the FINGERPRINT attribute so the
   STUN messages are disambiguated from the other protocol packets.

   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.  The Report transaction MUST be authenticated
   to prevent amplification attacks.  The client MUST add the
   FINGERPRINT attribute so the STUN messages are disambiguated from the
   other protocol packets.

   Then the client waits half the RTO, if it is known, or 250 ms after
   sending the last Probe Indication and then sends the Report Request
   to the server over UDP.

4.2.2.  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.







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4.2.3.  Receiving a Probe Indication and Report Request

   A server supporting this specification will keep the identifiers of
   all packets received in a chronologically ordered list.  The packets
   that are to be associated to a list are selected according to
   Section 5.2 of [RFC4821].  The same identifier can appear multiple
   times in the list because of retransmissions.  The maximum size of
   this list is calculated such 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 that
   is already full.

   A server receiving a Report Request MUST process it as specified in
   [RFC5389].

   The server creates a Report Response and adds an IDENTIFIERS
   attribute that contains the chronologically ordered list of all
   identifiers received so far.  The server MUST add the FINGERPRINT
   attribute.  The server then sends the response to the client.

   The exact content of the IDENTIFIERS attribute depends on what type
   of identifiers have been chosen for the protocol.  Each protocol
   adding PMTUD capabilities as specified by this specification MUST
   describe the format of the contents of the IDENTIFIERS attribute,
   unless it is using one of the formats described in this
   specification.  See Section 6.1 for details about the IDENTIFIERS
   attribute.

4.2.4.  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 identifiers for other packets sent
   before or after the Probe Indication can all be found, this is
   interpreted as a Probe Failure as defined in [RFC4821] Section 7.5.
   If the Report Transaction times out, this is interpreted as a Full-
   Stop Timeout, as defined in [RFC4821] Section 3.








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4.2.5.  Using Checksums as Packet Identifiers

   When using a checksum as a packet identifier, the client calculates
   the checksum for each packet sent over UDP that is not a STUN Probe
   Indication or Request and keeps this checksum in a chronologically
   ordered list.  The client also keeps the checksum of the STUN Probe
   Indication or Request sent in that same chronologically ordered list.
   The algorithm used to calculate the checksum is similar to the
   algorithm used for the FINGERPRINT attribute (i.e., the CRC-32 of the
   payload XOR'ed with the 32-bit value 0x5354554e).

   For each STUN Probe Indication or Request, the server retrieves the
   STUN FINGERPRINT value.  For all other packets, the server calculates
   the checksum as described above.  It puts these FINGERPRINT and
   checksum values in a chronologically ordered list that is sent back
   in the Report Response.

   The contents of the IDENTIFIERS attribute is a list of 4 byte
   numbers, each using the same encoding that is used for the contents
   of the FINGERPRINT attribute.

   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 is
   off-loaded to network hardware.

4.2.6.  Using Sequence Numbers as Packet Identifiers

   When using sequence numbers, a small header similar to the TURN
   ChannelData header is added in front of all packets that are not a
   STUN Probe Indication or Request.  The sequence number is
   monotonically incremented by one for each packet sent.  The most
   significant bit of the sequence number is always 0.  The server
   collects the sequence number of the packets sent, or the 4 first
   bytes of the transaction ID if a STUN Probe Indication or Request is
   sent.  In that case, the most significant bit of the 4 first bytes is
   set to 1.














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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             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|                      Sequence number                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   /                       Application Data                        /
   /                                                               /
   |                                                               |
   |                               +-------------------------------+
   |                               |
   +-------------------------------+

   The Channel Number is always 0xFFFF.  The header values are encoded
   using network order.

   The contents of the IDENTIFIERS attribute is a chronologically
   ordered list of 4 byte numbers, each containing either a sequence
   number, if the packet was not a STUN Probe Indication or Request, or
   the 4 first bytes of the transaction ID, with the most significant
   bit forced to 1, if the packet is a STUN Probe Indication or Request.

5.  Probe Support Signaling Mechanisms

   The PMTUD mechanism described in this document is intended to be used
   by any UDP-based protocols that do not have built-in PMTUD
   capabilities, irrespective of whether those UDP-based protocols are
   STUN-based or not.  So the manner in which a specific protocol
   discovers that it is safe to send PMTUD probes is largely dependent
   on the details of that specific protocol, with the exception of the
   Implicit Mechanism described below, which applies to any protocol.

5.1.  Explicit Probe Support Signaling Mechanism

   Some of these mechanisms can use a separate signalling mechanism (for
   instance, an SDP attribute in an Offer/Answer exchange [RFC3264]), or
   an optional flag that can be set in the protocol that is augmented
   with PMTUD capabilities.  STUN Usages that can benefit from PMTUD
   capabilities can signal in-band that they support probing by
   inserting a PMTUD-SUPPORTED attribute in some STUN methods.  The
   decision of which methods support this attribute is left to each
   specific STUN Usage.

   UDP-based protocols that want to use any of these mechanisms,
   including the PMTUD-SUPPORTED attribute, to signal PMTUD capabilities




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   MUST ensure that it cannot be used to launch an amplification attack.
   For example, using authentication can ensure this.

5.2.  Implicit Probe Support Signaling Mechanism

   As a result of the fact that all endpoints implementing this
   specification are both clients and servers, a Probe Request or
   Indication received by an endpoint acting as a server implicitly
   signals that this server can now act as a client and MAY send a Probe
   Request or Indication to probe the Path MTU in the reverse direction
   toward the former client, that will now be acting as a server.

   The Probe Request or Indication that are used to implicitly signal
   probing support in the reverse direction MUST be authenticated to
   prevent amplification attacks.

6.  STUN Attributes

6.1.  IDENTIFIERS

   The IDENTIFIERS attribute carries a chronologically ordered list of
   UDP packet identifiers.

   While Sections Section 4.2.5 and Section 4.2.6 describe two possible
   methods for acquiring and formatting the identifiers used for this
   purpose, ultimately each protocol has to define how these identifiers
   are acquired and formatted.  Therefore, the contents of the
   IDENTIFIERS attribute is opaque.

6.2.  PMTUD-SUPPORTED

   The PMTUD-SUPPORTED attribute indicates that its sender supports this
   specification.  This attribute has no value part and thus the
   attribute length field is 0.

7.  Security Considerations

   The PMTUD mechanism described in this document does not introduce any
   specific security considerations beyond those described in [RFC4821].

   The attacks described in Section 11 of [RFC4821] apply equally to the
   mechanism described in this document.

   The Simple Probing mechanism may be used without authentication
   because this usage by itself cannot trigger an amplification attack
   because the Probe Response is smaller than the Probe Request.  An
   unauthenticated Simple Probing mechanism cannot be used in




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   conjunction with the Implicit Probing Support Signaling mechanism in
   order to prevent amplification attacks.

8.  IANA Considerations

   This specification defines two new STUN methods 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 4.1 and Section 4.2 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 6.1.  IANA has allocated the comprehension-required codepoint
   0xXXXX for this attribute.

   This document also defines the PMTUD-SUPPORTED STUN attribute,
   described in Section 6.2.  IANA has allocated the comprehension-
   optional codepoint 0xXXXX for this attribute.

9.  References

9.1.  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>.

   [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>.





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9.2.  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.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264,
              DOI 10.17487/RFC3264, June 2002,
              <http://www.rfc-editor.org/info/rfc3264>.

   [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.

A.1.  Modifications between draft-ietf-tram-stun-pmtud-04 and draft-
      ietf-tram-stun-pmtud-03

   o  Modifications following Simon Perreault and Brandon Williams
      reviews.

A.2.  Modifications between draft-ietf-tram-stun-pmtud-03 and draft-
      ietf-tram-stun-pmtud-02

   o  Add new Overview of Operations section with ladder diagrams.

   o  Authentication is mandatory for the Complete Probing mechanism,
      optional for the Simple Probing mechanism.

   o  All the ICE specific text moves to a separate draft to be
      discussed in the ICE WG.

   o  The TURN usage is removed because probing between a TURN server
      and TURN client is not useful.






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   o  Any usage of PMTUD-SUPPORTED or other signaling mechanisms
      (formerly knows as discovery mechanisms) must now be
      authenticated.

   o  Both probing mechanisms are MTI in the server, the complete
      probing mechanism is MTI in the client.

   o  Make clear that stopping after 3 retransmission is done by
      changing the STUN parameter.

   o  Define the format of the attributes.

   o  Make clear that the specification is for any UDP protocol that
      does not already have PMTUD capabilities, not just STUN based
      protocols.

   o  Change the default delay to send the Report Request to 250 ms
      after the last Indication if the RTO is unknown.

   o  Each usage of this specification must the format of the
      IDENTIFIERS attribute contents.

   o  Better define the implicit signaling mechanism.

   o  Extend the Security Consideration section.

   o  Tons of nits.

A.3.  Modifications between draft-ietf-tram-stun-pmtud-02 and draft-
      ietf-tram-stun-pmtud-01

   o  Cleaned up references.

A.4.  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.5.  Modifications between draft-ietf-tram-stun-pmtud-00 and draft-
      petithuguenin-tram-stun-pmtud-01

   o  Adopted by WG - Text unchanged.







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A.6.  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.7.  Modifications between draft-petithuguenin-tram-stun-pmtud-00 and
      draft-petithuguenin-behave-stun-pmtud-03

   o  General refresh for republication.

A.8.  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.9.  Modifications between draft-petithuguenin-behave-stun-pmtud-02 and
      draft-petithuguenin-behave-stun-pmtud-01

   o  Defined checksum and sequential numbers as possible packet
      identifiers.

   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.








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A.10.  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.

Acknowledgements

   Thanks to Eilon Yardeni, Geir Sandbakken, Paal-Erik Martinsen,
   Tirumaleswar Reddy, Ram Mohan R, Simon Perreault, and Brandon
   Williams 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.

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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