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Re: GRE Extensions (Modified)
- To: Raymond Hsu <rhsu@qualcomm.com>
- Subject: Re: GRE Extensions (Modified)
- From: Rene Tio <tor@redback.com>
- Date: Fri, 17 Mar 2000 11:10:50 -0800
- Cc: Gopal Dommety <gdommety@cisco.com>, tsgp@3gpp2.org, udlr@sophia.inria.fr, msdp@antc.uoregon.edu, ipsec@lists.tislabs.com, MOBILE-IP@standards.nortelnetworks.com, l2tp@ipsec.org, tsga@3gpp2.org
- In-Reply-To: <200003171611.IAA17317@jittlov.qualcomm.com>; from rhsu@qualcomm.com on Fri, Mar 17, 2000 at 08:12:08AM -0800
- References: <LYR1158584-196913-2000.03.17-00.58.48--rhsu#qualcomm.com@3 <200003171611.IAA17317@jittlov.qualcomm.com>
On Fri, Mar 17, 2000 at 08:12:08AM -0800, Raymond Hsu wrote:
> Hi Gopal:
>
> In TR-45.6's R-P interface (aka A10 interface), we may use the first option
> in the direction
> from the PDSN to the PCF. In this direction, we've identified scenarios
> where some mobiles
> require in-sequence delivery and some don't. Since each mobile is
> identified by the Key field
> over the R-P interface, we need option 1. However, in the direction from
> the PCF to the PDSN,
> we don't have a strong requirement per mobile basis; thus, option 2 is
> adequate. Therefore,
> my recommendation is that both options should be allowed in the GRE draft.
I think if we plan the most limiting case (option 1, which we have at
least a few opinions is necessary) and allow for the not-so-limiting, both
cases will be covered.
IMHO the C, K, and S fields are a request for the other end to check, not a
requirement that the other end should send, i.e., if you configure a tunnel
to have checksums, you send checksums but don't require the other end to
send checksums (it's part of the "be liberal in what you receive" paradigm).
Thus in the PCF to PDSN direction you just don't configure sequence numbers
and everything Should Just Work.
Cheers,
Rene
ps/ Funny how the PPTP draft is vague on this as well, or at least my quick
glance did not find any statement on this matter. I don't think it
would work if you didn't have a sequence number per key though, as one
missed packet may cause you to turf packets across many PPP sessions.
> Regards,
>
> Raymond Hsu
>
> At 01:06 AM 3/17/00 -0800, Gopal Dommety wrote:
> >Hello:
> >
> >I have changed the sequence no to be 4 bytes. The changes request by
> >most have been made.
> >
> >A remining issue is regarding the behaviour when both sequence no and
> >the Key are present. There are two options:
> >
> >1. Have sequence no per Key. This will give better granularity with
> > added complexity of implementation.
> >
> >2. Sequence no for the tunnel irrespective of the Key.
> >
> >Let me know your opinion.
> >
> >Thanks
> >Gopal
> >
> >
> >Network Working Group Gopal Dommety
> >INTERNET DRAFT cisco Systems
> >Category: Standards Track March 2000
> >Title: draft-dommety-gre-ext-01.txt
> >
> >Expires October 2000
> >
> > Key and Sequence Number Extensions to GRE
> > draft-dommety-gre-ext-01.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) |
> > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> > | 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 a four byte feild and is inserted by
> > the encapsulator when Sequence Number Present Bit is set. The
> > 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 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. Note that packets without the sequence
> > bit set can be sent in between packets with the sequence bit set.
> >
> > The sequence number value ranges from 1 to 2**32-1. The first
> > datagram is sent with a sequence number of 1. The sequence
> > number is thus a free running counter represented modulo 2**32,
> > with the exception that 1 is used when modulo 2**32 results in 0
> > (i.e., rollover to 1 instead of 0).
> >
> > 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
> > 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 sequence
> > number of the received packet is lesser than or equal to the
> > sequence number of last successfully decapsulated
> > packet. The sequence number of a received message is considered
> > less than or equal to the last successfully received sequence number
> > if its value lies in the range of the last received sequence number
> > and the preceding 65534 values, inclusive.
> >
> >
> > If the received packet is an in-sequence packet, it is
> > successfully decapsulated. Note that the 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. Use of the sequence number option should be used
> > appropriately; in particular, it is a good idea a avoid using when
> > tunneling protocols that have higher layer in-order delivery
> > mechanisms or are tolerant to out-of-order delivery. If only at certain
> > instances the protocol being carried in the GRE tunnel requires
> > in-sequence delivery, only the corresponding packets encapsulated
> > in a GRE header can be sent with the sequence bit set. Mechanisims
> > to determine which packets need to be sent in-sequence and the
> > signaling mechanisims are outside the scope of this document.
> >
> >
> >
> >
> >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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> >
>