Subject: [MOBILE-IP] GRE Addendum

From: Gopal Dommety <[email-masked]>
Date: Tue, 7 Mar 2000 16:44:59 -0800

Hello:

        As requested  by IESG, I  written up a preliminary  version of
 the GRE addendum.  Please provide your comments.  As you go through the
 draft   at   places  identified   by   #   there   are  request   for
 comments. please give your opinion.

Thanks
Gopal

Network Working Group                                      Gopal Dommety
INTERNET DRAFT                                             cisco Systems
February 2000

Expires September 2000

                Key and Sequence Number Extensions to GRE
                    draft-dommety-gre-ext-00.txt

All comments/discussion of this draft should be directed to [email-masked]

Status of this Memo

   This document is an Internet Draft and is in full conformance with
   all provisions of Section 10 of RFC2026. Internet Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and working groups. Note that other groups may also distribute
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Abstract

   This  document describes extensions  by which  two fields,  Key and
Sequence Number, can be optionally carried in the GRE (Generic Routing
Encapsulation) Header  [1]. GRE specifies a  protocol for encapsulation
of an arbitrary network  layer protocol over another arbitrary network
layer  protocol.

Dommety                                                           [Page 1]

Internet Draft  Key and Sequence Number Extensions to GRE  February 2000

1. Introduction

   Current specification of Generic Routing Encapsulation [1] specifies
a protocol  for encapsulation of  an arbitrary network  layer protocol
over another arbitrary network layer protocol. This document describes
enhancements  by which  two fields,  Key and  Sequence Number,  can be
optionally carried  in the GRE  Header [1]. The  Key field is  used to
create separate sub-tunnels within  a GRE Tunnel. Sequence Number field
is used to maintain sequence of packets within a GRE Tunnel.

1.1. Specification Language

   The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
   this document are to be interpreted as described in RFC 2119 [3].

   In addition, the following words are used to signify the
   requirements of the specification.

   Silently discard
              The implementation discards the datagram without
              further processing, and without indicating an error
              to the sender.  The implementation SHOULD provide the
              capability of logging the error, including the contents
              of the discarded datagram, and SHOULD record the event
              in a statistics counter.

2. Extensions to GRE Header

   The GRE packet header[1] has the following format:

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |C|       Reserved0       | Ver |         Protocol Type         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      Checksum (optional)      |       Reserved1 (Optional)    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    The proposed GRE header will have the following format:

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |C| |K|S| Reserved0       | Ver |         Protocol Type         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      Checksum (optional)      |       Reserved1 (Optional)    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         Key (optional)                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Rx Sequence Number (Optional)| Tx Sequence Number (Optional) |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Key Present (bit 2)

      If the Key Present bit is set to 1, then it indicates that the Key
      field is present in the GRE header.  Otherwise, the Key field is
      not present in the GRE header.

      Sequence Number Present (bit 3)

      If the Sequence Number Present bit is set to 1, then it indicates
      that the Sequence Number field is present.  Otherwise, the
      Sequence Number field is not present in the GRE header.

      The  Key and Sequence Present bits are chosen to be  compatible
      with RFC 1701 [2].

2.1. Key Field (4 octets)

     The Key field contains a  four octet number which was inserted by
     the encapsulator. The actual method by which this Key is obtained
     is beyond the scope of this document.  Key field is intended to be
     used for  creating separate sub-tunnels within a  GRE Tunnel and the
     Key field identifies the sub-tunnel.

2.2. Sequence Number (4 octets)

    The Sequence Number  field is divided into two  sub-fields (Tx and
    Rx sequence number). These subfields are inserted by the encapsulator
    when Sequence Number Present Bit is set . Tx Sequence Number  MUST
    be used by the receiver to establish the  order in which  packets
    have been  transmitted from the  encapsulator  to  the  receiver.
    The intended  use  of  the Tx Sequence  Field is  to provide
    unreliable and in-order delivery.   If the Key  present bit (bit 2)
    is set, the sequence number is specific to the sub-tunnel identified
    by the Key field.

    The Tx sequence number  value ranges from 1 to  65535. The first
    datagram is sent with a Tx sequence number of 1. The Tx sequence
    number is thus a free running counter represented modulo 65536,
    with the exception that 1 is used when modulo 65536 results in 0
    (i.e., rollover to 1 instead of 0). The Rx Sequence number is set to 0.

#Q The Rx can be the Tx  sequence number of the last successfully decap
  pack.  And  say  that  how  you  use  this  info  is  implementation
  dependent. To avoid controversy I am currently saying Rx sequence no
  is set to 0. Comments?

    When the decapsulator receives an out-of sequence packet it SHOULD
    be silently discarded. Additionally, reordering of out-of sequence
    packets  MAY  be  performed   by  the  decapsulator  for  improved
    performance and  tolerance to reordering in the  network (since the
    state of the stateful compression or encryption is reset by packet
    loss, it  might help the  performance to tolerate some  amount of
    packet reordering in the network by buffering). Exact buffering
    schemes are outside the scope
    of  this  document. Note that the  Tx sequence number is used to detect
    lost packets and/or restore  the original sequence of packets that
    may have been reordered during transport.

   A packet  is considered an out-of-sequence packet  if the Tx sequence
   number  of  the  received packet  is  lesser than or equal to  the Tx
   sequence  number   of last  successfully  decapsulated
   packet. The  Tx sequence number  of a received message is considered
   less than or equal to the last successfully received Tx sequence number
   if its value lies in the range of the last received Tx sequence number
   and the preceding 32766 values, inclusive.  For example, if the last
   successfully received Tx sequence number was 15, then messages with Tx
   sequence numbers 1 through 15, as well as 32784 through 65535, would be
   considered less than or equal. Such a message would be considered an
   out-of-sequence packet and  ignored from processing.

    If the received packet is an in-sequence packet, it is successfully
    de capsulated. Note that  the TX sequence number is  used to detect
    lost packets and/or restore the original sequence of packets (with
    buffering) that may have been reordered during transport.

#C I have considered  trying to have a different  starting point for TX
sequence nos  during rollover and initial starting  point.  This would
let a node  identify if the other end  reset (like agent advertisement
sequence no to identify reboot and normal rollover). This is useful if
we keep turning on and off sequence nos option in a tunnel. Comments?

3. IANA Considerations

4. Acknowledgments

   The author  would like to thank  .......................  for their
   useful discussions.

5. References

   [1] Farinacci,  D., Li,  T., Hnaks, S.,  Meyer, D. and  Traina, P.,
   "Generic           Routing           Encapsulation          (GRE),"
   draft-meyer-gre-update-03.txt, January 2000.

   [2]  Hanks, S.,  Li,  T,  Farinacci, D.,  and  P. Traina,  "Generic
   Routing Encapsulation",  RFC 1701, NetSmiths,  Ltd., and cisco Systems,
   October 1994.

   [3] Bradner S., "Key words for use in RFCs to Indicate Requirement
       Levels", RFC 2119, March 1997.

Dommety                                                 [Page 4]

Internet Draft   Key and Sequence Number extensions to GRE   February 2000

Author Information

   Gopal Dommety
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, CA 95134
   e-mail: [email-masked]

Dommety

Thank You.
Regards,
Gopal
-------------------------------------------------------------------------------------------------------------

Gopal Dommety
408 525 1404
[email-masked]
Cisco Systems, San Jose, CA, 95051