Additional Considerations for UDP Encapsulation of Stream Control Transmission Protocol (SCTP) Packets
draft-tuexen-tsvwg-sctp-udp-encaps-cons-07

Network Working Group                                           M. Tüxen
Internet-Draft                           Münster Univ. of Appl. Sciences
Updates: 6951 (if approved)                                R. R. Stewart
Intended status: Standards Track                           Netflix, Inc.
Expires: 11 September 2023                                 10 March 2023

   Additional Considerations for UDP Encapsulation of Stream Control
                  Transmission Protocol (SCTP) Packets
               draft-tuexen-tsvwg-sctp-udp-encaps-cons-07

Abstract

   RFC 6951 specifies the UDP encapsulation of SCTP packets.  The
   described handling of received packets requires the check of the
   verification tag.  However, RFC 6951 misses a specification of the
   handling of received packets for which this check is not possible.

   This document updates RFC 6951 by specifying the handling of received
   packets for which the verification tag can not be checked.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on 11 September 2023.

Copyright Notice

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   extracted from this document must include Revised BSD License text as
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Handling of Out of the Blue Packets . . . . . . . . . . . . .   3
   4.  Handling of SCTP Packets Containing an INIT Chunk Matching an
           Existing Associations . . . . . . . . . . . . . . . . . .   3
   5.  Middlebox Considerations  . . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   [RFC6951] specifies the UDP encapsulation of SCTP packets.  To be
   able to adopt automatically to changes of the remote UDP
   encapsulation port number, it is updated when processing received
   packets.  This includes automatic enabling and disabling of UDP
   encapsulation.

   Section 5.4 of [RFC6951] describes the processing of received packets
   and requires the check of the verification tag before updating the
   remote UDP encapsulation port and the possible enabling or disabling
   of UDP encapsulation.

   [RFC6951] basically misses a description of the handling of received
   packets where checking the verification tag is not possible.  This
   includes packets for which no association can be found and packets
   containing an INIT chunk, since the verification tag of these packets
   is 0.

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.

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3.  Handling of Out of the Blue Packets

   If the processing of an out of the blue packet requires the sending
   of a packet in response according to the rules specified in
   Section 8.4 of [RFC9260], the following rules apply:

   1.  If the received packet was encapsulated in UDP, the response
       packets MUST also be encapsulated in UDP.  The UDP source port
       and UDP destination port used for sending the response packet are
       the UDP destination port and UDP source port of the received
       packet.

   2.  If the received packet was not encapsulated in UDP, the response
       packet MUST NOT be encapsulated in UDP.

   Please note that in these cases a check of the verification tag is
   not possible.

4.  Handling of SCTP Packets Containing an INIT Chunk Matching an
    Existing Associations

   SCTP packets containing an INIT chunk have the verification tag 0 in
   the common header.  Therefore the verification tag can't be checked.

   The following rules apply when processing the received packet:

   1.  The remote UDP encapsulation port for the source address of the
       received SCTP packet MUST NOT be updated if the encapsulation of
       outgoing packets is enabled and the received SCTP packet is
       encapsulated.

   2.  The UDP encapsulation for outgoing packets towards the source
       address of the received SCTP packet MUST NOT be enabled, if it is
       disabled and the received SCTP packet is encapsulated.

   3.  The UDP encapsulation for outgoing packets towards the source
       address of the received SCTP packet MUST NOT be disabled, if it
       is enabled and the received SCTP packet is not encapsulated.

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   4.  If the UDP encapsulation for outgoing packets towards the source
       address of the received SCTP packet is disabled and the received
       SCTP packet is encapsulated, an SCTP packet containing an ABORT
       chunk MUST be sent.  The ABORT chunk MAY include the error cause
       defined below indicating an "Restart of an Association with New
       Encapsulation Port".  This packet containing the ABORT chunk MUST
       be encapsulated in UDP.  The UDP source port and UDP destination
       port used for sending the packet containing the ABORT chunk are
       the UDP destination port and UDP source port of the received
       packet containing the INIT chunk.

   5.  If the UDP encapsulation for outgoing packets towards the source
       address of the received SCTP packet is disabled and the received
       SCTP packet is not encapsulated, the processing defined in
       [RFC9260] MUST be performed.  If a packet is sent in response, it
       MUST NOT be encapsulated.

   6.  If the UDP encapsulation for outgoing packets towards the source
       address of the received SCTP packet is enabled and the received
       SCTP packet is not encapsulated, an SCTP packet containing an
       ABORT chunk MUST be sent.  The ABORT chunk MAY include the error
       cause defined below indicating an "Restart of an Association with
       New Encapsulation Port".  This packet containing the ABORT chunk
       MUST NOT be encapsulated in UDP.

   7.  If the UDP encapsulation for outgoing packets towards the source
       address of the received SCTP packet is enabled and the received
       SCTP packet is encapsulated, but the UDP source port of the
       received SCTP packet is not equal to the remote UDP encapsulation
       port for the source address of the received SCTP packet, an SCTP
       packet containing an ABORT chunk MUST be sent.  The ABORT chunk
       MAY include the error cause defined below indicating an "Restart
       of an Association with New Encapsulation Port".  This packet
       containing the ABORT chunk MUST be encapsulated in UDP.  The UDP
       source port and UDP destination port used for sending the packet
       containing the ABORT chunk are the UDP destination port and UDP
       source port of the received packet containing the INIT chunk.

   8.  If the UDP encapsulation for outgoing packets towards the source
       address of the received SCTP packet is enabled and the received
       SCTP packet is encapsulated and the UDP source port of the
       received SCTP packet is equal to the remote UDP encapsulation
       port for the source address of the received SCTP packet, the
       processing defined in [RFC9260] MUST be performed.  If a packet
       is sent in response, it MUST be encapsulated.  The UDP source
       port and UDP destination port used for sending the packet
       containing the ABORT chunk are the UDP destination port and UDP
       source port of the received packet containing the INIT chunk.

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   The error cause indicating an "Restart of an Association with New
   Encapsulation Port" is defined by the following figure.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Cause Code = 14        |       Cause Length = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Current Encapsulation Port  |     New Encapsulation Port    |
   +-------------------------------+-------------------------------+

      Figure 1: Restart of an Association with New Encapsulation Port
                                Error Cause

   Cause Code: 2 bytes (unsigned integer)
      This field holds the IANA defined cause code for the "Restart of
      an Association with New Encapsulation Port" error cause.  IANA is
      requested to assign the value 14 for this cause code.

   Cause Length: 2 bytes (unsigned integer)
      This field holds the length in bytes of the error cause; the value
      MUST be 8.

   Current Encapsulation Port: 2 bytes (unsigned integer)
      This field holds the remote encapsulation port currently being
      used for the destination address the received packet containing
      the INIT chunk was sent from.  If the UDP encapsulation for
      destination address is currently disabled, 0 is used.

   New Encapsulation Port: 2 bytes (unsigned integer)
      If the received SCTP packet containing the INIT chunk is
      encapsulated in UDP, this field holds the UDP source port number
      of the UDP packet.  If the received SCTP packet is not
      encapsulated in UDP, this field is 0.

   All transported integer numbers are in "network byte order" a.k.a.,
   Big Endian.

5.  Middlebox Considerations

   Middleboxes often use different timeouts for UDP based flows than for
   other flows.  Therefore the HEARTBEAT.Interval parameter SHOULD be
   lowered to 15 seconds when UDP encapsulation is used.

6.  IANA Considerations

   [NOTE to RFC-Editor: "RFCXXXX" is to be replaced by the RFC number
   you assign this document.]

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   [NOTE to RFC-Editor: The requested values for the cause code are
   tentative and to be confirmed by IANA.]

   This document (RFCXXXX) is the reference for the registration
   described in this section.

   A new error cause code has to be assigned by IANA.  This requires an
   additional line in the "Error Cause Codes" registry for SCTP:

            +=======+=============================+===========+
            | Value | Cause Code                  | Reference |
            +=======+=============================+===========+
            | 14    | Restart of an Association   | [RFCXXXX] |
            |       | with New Encapsulation Port |           |
            +-------+-----------------------------+-----------+

              Table 1: New entry in Error Cause Codes registry

7.  Security Considerations

   This document does not change the considerations given in [RFC6951].

   However, not following the procedures given in this document might
   allow an attacker to take over SCTP associations.  The attacker needs
   only to share the IP address of an existing SCTP association.

   If firewalls will be applied at the SCTP association level, they have
   to take the UDP encapsulation into account.

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>.

   [RFC6951]  Tuexen, M. and R. Stewart, "UDP Encapsulation of Stream
              Control Transmission Protocol (SCTP) Packets for End-Host
              to End-Host Communication", RFC 6951,
              DOI 10.17487/RFC6951, May 2013,
              <https://www.rfc-editor.org/info/rfc6951>.

   [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>.

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   [RFC9260]  Stewart, R., Tüxen, M., and K. Nielsen, "Stream Control
              Transmission Protocol", RFC 9260, DOI 10.17487/RFC9260,
              June 2022, <https://www.rfc-editor.org/info/rfc9260>.

Acknowledgments

   The authors wish to thank Georgios Papastergiou for the initial
   problem report.

   The authors wish to thank Irene Rüngeler and Felix Weinrank for their
   invaluable comments.

   This work has received funding from the European Union's Horizon 2020
   research and innovation programme under grant agreement No. 644334
   (NEAT).  The views expressed are solely those of the author(s).

Authors' Addresses

   Michael Tüxen
   Münster University of Applied Sciences
   Stegerwaldstrasse 39
   48565 Steinfurt
   Germany
   Email: tuexen@fh-muenster.de

   Randall R. Stewart
   Netflix, Inc.
   15214 Pendio Drive
   Bella Collina, FL 34756
   United States of America
   Email: randall@lakerest.net

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