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Network Working Group Stan Hanks
INTERNET DRAFT Technology Transfer Associates
Tony Li
Dino Farinacci
Paul Traina
cisco Systems
September 8, 1993
Generic Routing Encapsulation over IPv4 networks
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard. Distribution of this memo is
unlimited.
This document is an Internet Draft. Internet Drafts are working
documents of the Internet Engineering Task Force (IETF), its Areas,
and its 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. Internet Drafts may be updated, replaced, or obsoleted by
other documents at any time. It is not appropriate to use Internet
Drafts as reference material or to cite them other than as a "working
draft" or "work in progress".
Introduction
In an earlier memo[HLFT], 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.
Expiration Date February 1994 [Page 1]
Internet Draft August 1993
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.
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.
Expiration Date February 1994 [Page 2]
Internet Draft August 1993
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
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
Expiration Date February 1994 [Page 3]
Internet Draft August 1993
Security considerations are not discussed in this memo.
Authors' Addresses:
Stanley P. Hanks
Technology Transfer Associates
P.O. Box 2087
Bellaire TX, 77402
stan@tta.com
Tony Li
cisco Systems, Inc.
1525 O'Brien Drive
Menlo Park, CA 94025
tli@cisco.com
Dino Farinacci
cisco Systems, Inc.
1525 O'Brien Drive
Menlo Park, CA 94025
dino@cisco.com
Paul Traina
cisco Systems, Inc.
1525 O'Brien Drive
Menlo Park, CA 94025
pst@cisco.com
References
HLFT Hanks, S., Li, T, Farinacci, D., Traina, P. "Generic Routing Encap-
sulation", Work in progress
Expiration Date February 1994 [Page 4]