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GRE extensions

To: udlr@sophia.inria.fr
Subject: GRE extensions
From: Gopal Dommety <gdommety@cisco.com>
Date: Fri, 10 Mar 2000 09:45:57 -0800
Cc: msdp@antc.uoregon.edu, ipsec@lists.tislabs.com
Sender: owner-ipsec@lists.tislabs.com

Hello:

I am attaching the GRE addendum/extensions. As you go through the
draft at places identified by # there are request for comments. I have
split the sequence no into two subfeilds (the other option is to define an
acknowledgement like PPTP WHEN such a need it felt).

Please send your comments to gre@ops.ietf.org mailing list. you can
subscribe to this mailing list by sending an email to
gre-request@ops.ietf.org

Thanks
Gopal

Network Working Group Gopal Dommety
INTERNET DRAFT cisco Systems
March 2000

Expires October 2000

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

Status of this Memo

This document is a submission by the Network Working Group of the
Internet Engineering Task Force (IETF). Comments should be submitted
to the gre@ops.ietf.org mailing list.

Distribution of this memo is unlimited.

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
working documents as Internet Drafts.

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."

The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.

The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.

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. 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. Since
there is no security it is easy for others to reset the sequence
also. Comments?

3. IANA Considerations

4. Acknowledgments

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: gdommety@cisco.com

Dommety

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

Gopal Dommety
408 525 1404
gdommety@cisco.com
Cisco Systems, San Jose, CA, 95051

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