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Versions: 00 01                                                         
INTERNET-DRAFT                                                T. Herbert
Intended Status: Proposed Standard                              Facebook
Expires: April 2016

                                                        October 19, 2015


             Checksum option for Generic UDP Encapsulation
                        draft-herbert-guecsum-01


Abstract

   This specification defines the Generic UDP Encapsulation (GUE)
   checksum and an associated header option. This checksum covers the
   GUE header, IP addresses, UDP ports, and optionally all or part of
   the encapsulated payload. It provides verification of protocol header
   elements, and is particularly relevant in the case where the UDP
   checksum is set to zero.
Status of this Memo

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

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Copyright and License Notice

   Copyright (c) 2015 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



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   (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
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   described in the Simplified BSD License.


Table of Contents

   1  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2  Option format . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3 Operation  . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.1. Requirements  . . . . . . . . . . . . . . . . . . . . . . .  4
     3.2. GUE pseudo header . . . . . . . . . . . . . . . . . . . . .  5
     3.3. Checksum computation  . . . . . . . . . . . . . . . . . . .  6
     3.4. Transmitter operation . . . . . . . . . . . . . . . . . . .  6
     3.5. Receiver operation  . . . . . . . . . . . . . . . . . . . .  7
   4  Security Considerations . . . . . . . . . . . . . . . . . . . .  7
   5  IANA Considerations . . . . . . . . . . . . . . . . . . . . . .  7
   6  References  . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     6.1  Normative References  . . . . . . . . . . . . . . . . . . .  7
     6.2  Informative References  . . . . . . . . . . . . . . . . . .  8
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . .  8


























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1  Introduction

   The UDP checksum provides a method to detected corrupted packets
   [RFC0768]. The covered checksum includes a pseudo header consisting
   of IP addresses, payload length, and protocol number (17 for UDP).
   The pseudo header checksum protects against misdelivery due to
   corrupted IP addresses, as well as some other issues occurring when
   the IP header is corrupted. The IPv4 header contains its own header
   checksum, however IPv6 does not. In the latter case there is
   motivation when using UDP to enable the UDP checksum to protect
   against misdelivery due to address corruption.

   For UDP tunnels, there may be performance disadvantages in enabling
   the UDP checksum. This may, for instance, be an issue in switch
   hardware which might only have access to a limited portion of the
   packet for inspection. Therefore, there is motivation to use zero
   checksums with UDP tunneling. The requirements and applicability of
   using zero UDP checksums with IPv6 are in RFC 6935 [RFC6935] and RFC
   6936 [RFC6936].

   In this document we define the Generic UDP Encapsulation [GUE]
   checksum. This provides a checksum that covers the GUE header and a
   GUE pseudo header. The GUE pseudo header includes the corresponding
   IP addresses as well as the UDP ports of the encapsulating headers.
   This checksum should provide adequate protection against address
   corruption in IPv6 when the UDP checksum is zero. Additionally, the
   GUE checksum provides protection of the GUE header when the UDP
   checksum is set to zero with either IPv4 or IPv6. In particular, the
   GUE checksum can provide protection for some sensitive data, such as
   the virtual network identifier [GUENVO3], which when corrupted could
   lead to misdelivery of the packet.

   The GUE header checksum may optionally cover all or part of the
   encapsulated payload. This is similar to the model of UDP-Lite
   [RFC3828] where an additional field indicates the portion of the
   payload that is covered in the checksum.

2  Option format

   The GUE header checksum is sent in an optional field in the GUE
   header. The format of the GUE checksum option field is:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Checksum           |        Payload coverage       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




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      o Checksum: GUE checksum. This checksum covers the GUE header, the
        GUE pseudo header, and optionally all or part of the payload
        (encapsulated packet).

      o Payload coverage: Number of bytes of payload to cover in the
        checksum. Zero indicates that the checksum only covers the GUE
        header and GUE pseudo header. If the value is greater than the
        encapsulated payload length, the packet must be dropped. The
        payload length is UDP_length - 12 - (Hlen * 4).


   The format of the checksum option within the GUE header is:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Source port            |      Destination port         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Length              |          Checksum             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0x0|C|   Hlen  |  Proto/ctype  |V|SEC|K|      Flags          |P|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~               VNI and Security fields (optional)              ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Checksum            |        Payload coverage       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Private flags(optional)                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                   Private fields (optional)                   ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      o K bit - Indicates presence of the checksum and payload coverage
        fields.

3 Operation

3.1. Requirements

   The GUE header checksum must be set on transmit when using a zero UDP
   checksum with IPv6.

   The GUE header checksum must be set when the UDP checksum is zero for
   IPv4 if the GUE header includes data that when corrupted can lead to
   misdelivery or other serious consequences, and there is no other



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   mechanism that provides protection (no security field for instance).
   Otherwise the GUE header checksum should be used with IPv4 when the
   UDP checksum is zero.

   The GUE header checksum should not be set when the UDP checksum is
   non-zero. In this case the UDP checksum provides adequate protection
   and this avoids convolutions when a packet traverses NAT that does
   address translation (in that case the UDP checksum is required).

3.2. GUE pseudo header

   The GUE pseudo header checksum is included in the GUE checksum to
   provide protection for the IP and UDP header elements which when
   corrupted could lead to misdelivery of the GUE packet. The GUE pseudo
   header checksum is similar to the standard IP pseudo header defined
   in [RFC0768] and [RFC0793] for IPv4, and in [RFC2460] for IPv6.

   The GUE pseudo header for IPv4 is:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Source Address                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Destination Address                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Source port            |      Destination port         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The GUE pseudo header for IPv6 is:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                         Source Address                        +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                      Destination Address                      +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Source port            |      Destination port         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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   Note that the GUE pseudo header does not include payload length or
   protocol as in the standard IP pseudo headers. The length field is
   deemed unnecessary because:

      o If the length is corrupted this will usually be detected by a
        checksum validation failure on the inner packet.

      o Fragmentation of packets in a tunnel should occur on the inner
        packet before being encapsulated. GUE packets are not expected
        to be fragmented when using IPv6. See RFC6936 for considerations
        of payload length and IPv6 checksum.

      o A corrupted length field in itself should not lead to
        misdelivery of a packet.

      o Without the length field, the GUE pseudo header checksum is the
        same for all packets of flow. This is a useful property for
        optimizations such as TCP Segment Offload (TSO).

3.3. Checksum computation

   The GUE checksum is computed and verified following the standard
   process for computing the Internet checksum [RFC1071]. Checksum
   computation may be optimized per the mathematical properties
   including parallel computation and incremental updates.

3.4. Transmitter operation

   The procedure for setting the GUE checksum on transmit is:

      1) Create the GUE header including the checksum and payload
         coverage fields. The checksum field is initially set to zero.

      2) Calculate the 1's complement checksum of the GUE header from
         the start (GUE version) through the its length as indicated in
         GUE Hlen.

      3) Calculate the checksum of the GUE pseudo header for IPv4 or
         IPv6.

      4) Calculate checksum of payload portion if payload coverage is
         enabled (payload coverage field is non-zero). If the length of
         the payload coverage is odd, logically append a single zero
         byte for the purposes of checksum calculation.

      5) Add and fold the computed checksums for the GUE header, GUE
         pseudo header and payload coverage. Set the result in the GUE
         checksum field.



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3.5. Receiver operation

   If the GUE checksum is option is present, the receiver must validate
   the checksum before processing any other fields or accepting the
   packet.

   The procedure for verifying the checksum is:

      1) If the payload coverage length is greater than the length of
         the encapsulated payload then drop the packet. The length of
         the encapsulated payload is: UDP_length - 12 - (Hlen * 4).

      2) Calculate the checksum of the GUE header from the start of the
         header to the end as indicated by Hlen.

      3) Calculate the checksum of the appropriate GUE pseudo header.

      4) Calculate the checksum of payload if payload coverage is
         enabled (payload coverage is non-zero). If the length of the
         payload coverage is odd logically append a single zero byte for
         the purposes of checksum calculation.

      5) Sum the computed checksums for the GUE header, GUE pseudo
         header, and payload coverage. If the result is all 1 bits (-0
         in 1's complement arithmetic), the checksum is valid and the
         packet is accepted; otherwise the checksum is considered
         invalid and the packet must be dropped.

4  Security Considerations

         The checksum option is only a mechanism for corruption
         detection, it is not a security mechanism. To provide integrity
         checks or authentication of the GUE header, the GUE security
         option should be used [GUESEC].

5  IANA Considerations

         There are no IANA considerations in this specification. One of
         the GUE reserved flag bits is allocated to indicate presence of
         the checksum field.

6  References

6.1  Normative References

   [GUE]     Generic UDP Encapsulation draft-ietf-nvo3-gue-01





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   [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September
             1981.

   [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
             Communication Layers", STD 3, RFC 1122, October 1989.

   [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
             August 1980.

   [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
             (IPv6) Specification", RFC 2460, December 1998.

   [RFC1071] Braden, R., Borman, D., and C. Partridge, "Computing the
             Internet checksum", RFC 1071, September 1988.

6.2  Informative References

   [RFC6935] Eubanks, M. Chimento, P., and M. Westerlund, "IPv6 and UDP
             Checksums for Tunneled Packets", RFC 6935, April 2013.

   [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement
             for the Use of IPv6 UDP Datagrams with Zero Checksums", RFC
             6936, April 2013.

   [RFC3828] Larzon, L-A., Degermark, M., Pink, S., Jonsson, L-E., Ed.,
             and G. Fairhurst, Ed., "The Lightweight User Datagram
             Protocol (UDP-Lite)", RFC 3828, July 2004.

   [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC
             793, September 1981.

   [GUENVO3]  Generic UDP Encapsulation (GUE) for Network Virtualization
             Overlay draft-hy-nvo3-gue-4-nvo-00

   [GUESEC] Generic UDP Encapsulation (GUE) for Secure Transport draft-
             hy-gue-4-secure-transport-00



Author's Address

   Tom Herbert
   Facebook
   Menlo Park, CA
   USA

   Email: tom@herbertland.com




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