GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc1702

Network Working Group S. Hanks Request for Comments: 1702 NetSmiths, Ltd. Category: Informational T. Li

                                                          D. Farinacci
                                                             P. Traina
                                                         cisco Systems
                                                          October 1994
          Generic Routing Encapsulation over IPv4 networks

Status of this Memo

 This memo provides information for the Internet community.  This memo
 does not specify an Internet standard of any kind.  Distribution of
 this memo is unlimited.

Introduction

 In an earlier memo [RFC 1701], we described GRE, a mechanism for
 encapsulating arbitrary packets within an arbitrary transport
 protocol.  This is a companion memo which describes the use of GRE
 with IP.  This memo addresses the case of using IP as the delivery
 protocol or the payload protocol and the special case of IP as both
 the delivery and payload.  This memo also describes using IP
 addresses and autonomous system numbers as part of a GRE source
 route.

IP as a delivery protocol

 GRE packets which are encapsulated within IP will use IP protocol
 type 47.

IP as a payload protocol

 IP packets will be encapsulated with a Protocol Type field of 0x800.
 For the Address Family value of 0x800, the Routing Information field
 will consist of a list of IP addresses and indicates an IP source
 route.  The first octet of the Routing Information field constitute a
 8 bit integer offset from the start of the Source Route Entry (SRE),
 called the SRE Offset.  The SRE Offset indicates the first octet of
 the next IP address.  The SRE Length field consists of the total
 length of the IP Address List in octets.

Hanks, Li, Farinacci & Traina [Page 1] RFC 1702 GRE over IPv4 networks October 1994

 This has the form:
     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |        Address Family         |  SRE Offset   |  SRE Length   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        IP Address List ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 For the Address Family value of 0xfffe, the Routing Information field
 will consist of a list of Autonomous System numbers and indicates an
 AS source route.  The third octet of the Routing Information field
 contains an 8 bit unsigned integer offset from the start of the
 Source Route Entry (SRE), called the SRE Offset.  The SRE Offset
 indicates the first octet of the next AS number.  THe SRE Length
 field consists of the total length of the AS Number list in octets.
     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |        Address Family         |  SRE Offset   |  SRE Length   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         AS Number List ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

IP as both delivery and payload protocol

 When IP is encapsulated in IP, the TTL, TOS, and IP security options
 MAY be copied from the payload packet into the same fields in the
 delivery packet.  The payload packet's TTL MUST be decremented when
 the packet is decapsulated to insure that no packet lives forever.

IP source routes

 When a system is processing a SRE with an Address Family indicating
 an IP source route, it MUST use the SRE Offset to determine the next
 destination IP address.  If the next IP destination is this system,
 the SRE Offset field should be increased by four (the size of an IP
 address).  If the SRE Offset is equal to the SRE Length in this SRE,
 then the Offset field in the GRE header should be adjusted to point
 to the next SRE (if any).  This should be repeated until the next IP
 destination is not this system or until the entire SRE has been
 processed.
 If the source route is incomplete, then the Strict Source Route bit
 is checked.  If the source route is a strict source route and the
 next IP destination is NOT an adjacent system, the packet MUST be

Hanks, Li, Farinacci & Traina [Page 2] RFC 1702 GRE over IPv4 networks October 1994

 dropped.  Otherwise, the system should use the IP address indicated
 by the Offset field to replace the destination address in the
 delivery header and forward the packet.

Autonomous system source routes

 When a system is processing a SRE with an Address Family indicating
 an AS source route, it MUST use the SRE Offset field to determine the
 next autonomous system.  If the next autonomous system is the local
 autonomous system, the SRE Offset field should be increased by two
 (the size of an autonomous system number).  If the SRE Offset is
 equal to the SRE Length in this SRE, then the Offset field in the GRE
 header should be adjusted to point to the next SRE (if any).  This
 should be repeated until the next autonomous system number is not
 equal to the local autonomous system number or until the entire SRE
 has been processed.
 If the source route is incomplete, then the Strict Source Route bit
 is checked.  If the source route is a strict source route and the
 next autonomous system is NOT an adjacent autonomous system, the
 packet should be dropped.  Otherwise, the system should use the
 autonomous system number indicated by the SRE Offset field to replace
 the destination address in the delivery header and forward the
 packet.  The exact mechanism for determining the next delivery
 destination address given the AS number is outside of the scope of
 this document.

Security Considerations

 Security issues are not discussed in this memo.

Hanks, Li, Farinacci & Traina [Page 3] RFC 1702 GRE over IPv4 networks October 1994

Authors' Addresses

 Stan Hanks
 NetSmiths, Ltd.
 2025 Lincoln Highway
 Edison, NJ 08817
 EMail: stan@netsmiths.com
 Tony Li
 cisco Systems, Inc.
 1525 O'Brien Drive
 Menlo Park, CA 94025
 EMail: tli@cisco.com
 Dino Farinacci
 cisco Systems, Inc.
 1525 O'Brien Drive
 Menlo Park, CA 94025
 EMail: dino@cisco.com
 Paul Traina
 cisco Systems, Inc.
 1525 O'Brien Drive
 Menlo Park, CA 94025
 EMail: pst@cisco.com

References

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

Hanks, Li, Farinacci & Traina [Page 4]

/data/webs/external/dokuwiki/data/pages/rfc/rfc1702.txt · Last modified: 1994/10/20 20:05 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki