228 lines
7.1 KiB
Plaintext
228 lines
7.1 KiB
Plaintext
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Network Working Group S. Hanks
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Request for Comments: 1702 NetSmiths, Ltd.
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Category: Informational T. Li
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D. Farinacci
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P. Traina
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cisco Systems
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October 1994
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Generic Routing Encapsulation over IPv4 networks
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Status of this Memo
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This memo provides information for the Internet community. This memo
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does not specify an Internet standard of any kind. Distribution of
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this memo is unlimited.
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Introduction
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In an earlier memo [RFC 1701], we described GRE, a mechanism for
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encapsulating arbitrary packets within an arbitrary transport
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protocol. This is a companion memo which describes the use of GRE
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with IP. This memo addresses the case of using IP as the delivery
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protocol or the payload protocol and the special case of IP as both
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the delivery and payload. This memo also describes using IP
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addresses and autonomous system numbers as part of a GRE source
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route.
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IP as a delivery protocol
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GRE packets which are encapsulated within IP will use IP protocol
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type 47.
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IP as a payload protocol
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IP packets will be encapsulated with a Protocol Type field of 0x800.
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For the Address Family value of 0x800, the Routing Information field
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will consist of a list of IP addresses and indicates an IP source
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route. The first octet of the Routing Information field constitute a
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8 bit integer offset from the start of the Source Route Entry (SRE),
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called the SRE Offset. The SRE Offset indicates the first octet of
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the next IP address. The SRE Length field consists of the total
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length of the IP Address List in octets.
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Hanks, Li, Farinacci & Traina [Page 1]
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RFC 1702 GRE over IPv4 networks October 1994
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This has the form:
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0 1 2 3
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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
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Address Family | SRE Offset | SRE Length |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| IP Address List ...
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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For the Address Family value of 0xfffe, the Routing Information field
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will consist of a list of Autonomous System numbers and indicates an
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AS source route. The third octet of the Routing Information field
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contains an 8 bit unsigned integer offset from the start of the
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Source Route Entry (SRE), called the SRE Offset. The SRE Offset
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indicates the first octet of the next AS number. THe SRE Length
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field consists of the total length of the AS Number list in octets.
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0 1 2 3
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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
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Address Family | SRE Offset | SRE Length |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| AS Number List ...
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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IP as both delivery and payload protocol
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When IP is encapsulated in IP, the TTL, TOS, and IP security options
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MAY be copied from the payload packet into the same fields in the
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delivery packet. The payload packet's TTL MUST be decremented when
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the packet is decapsulated to insure that no packet lives forever.
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IP source routes
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When a system is processing a SRE with an Address Family indicating
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an IP source route, it MUST use the SRE Offset to determine the next
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destination IP address. If the next IP destination is this system,
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the SRE Offset field should be increased by four (the size of an IP
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address). If the SRE Offset is equal to the SRE Length in this SRE,
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then the Offset field in the GRE header should be adjusted to point
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to the next SRE (if any). This should be repeated until the next IP
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destination is not this system or until the entire SRE has been
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processed.
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If the source route is incomplete, then the Strict Source Route bit
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is checked. If the source route is a strict source route and the
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next IP destination is NOT an adjacent system, the packet MUST be
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Hanks, Li, Farinacci & Traina [Page 2]
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RFC 1702 GRE over IPv4 networks October 1994
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dropped. Otherwise, the system should use the IP address indicated
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by the Offset field to replace the destination address in the
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delivery header and forward the packet.
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Autonomous system source routes
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When a system is processing a SRE with an Address Family indicating
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an AS source route, it MUST use the SRE Offset field to determine the
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next autonomous system. If the next autonomous system is the local
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autonomous system, the SRE Offset field should be increased by two
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(the size of an autonomous system number). If the SRE Offset is
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equal to the SRE Length in this SRE, then the Offset field in the GRE
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header should be adjusted to point to the next SRE (if any). This
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should be repeated until the next autonomous system number is not
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equal to the local autonomous system number or until the entire SRE
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has been processed.
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If the source route is incomplete, then the Strict Source Route bit
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is checked. If the source route is a strict source route and the
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next autonomous system is NOT an adjacent autonomous system, the
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packet should be dropped. Otherwise, the system should use the
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autonomous system number indicated by the SRE Offset field to replace
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the destination address in the delivery header and forward the
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packet. The exact mechanism for determining the next delivery
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destination address given the AS number is outside of the scope of
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this document.
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Security Considerations
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Security issues are not discussed in this memo.
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Hanks, Li, Farinacci & Traina [Page 3]
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RFC 1702 GRE over IPv4 networks October 1994
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Authors' Addresses
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Stan Hanks
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NetSmiths, Ltd.
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2025 Lincoln Highway
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Edison, NJ 08817
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EMail: stan@netsmiths.com
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Tony Li
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cisco Systems, Inc.
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1525 O'Brien Drive
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Menlo Park, CA 94025
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EMail: tli@cisco.com
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Dino Farinacci
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cisco Systems, Inc.
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1525 O'Brien Drive
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Menlo Park, CA 94025
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EMail: dino@cisco.com
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Paul Traina
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cisco Systems, Inc.
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1525 O'Brien Drive
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Menlo Park, CA 94025
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EMail: pst@cisco.com
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References
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RFC 1701
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Hanks, S., Li, T, Farinacci, D., and P. Traina, "Generic Routing
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Encapsulation", RFC 1701, NetSmiths, Ltd., and cisco Systems,
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October 1994.
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Hanks, Li, Farinacci & Traina [Page 4]
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