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diff --git a/rfc/rfc1701.txt b/rfc/rfc1701.txt new file mode 100644 index 00000000..60a0e9b9 --- /dev/null +++ b/rfc/rfc1701.txt @@ -0,0 +1,451 @@ + + + + + + +Network Working Group S. Hanks +Request for Comments: 1701 NetSmiths, Ltd. +Category: Informational T. Li + D. Farinacci + P. Traina + cisco Systems + October 1994 + + + Generic Routing Encapsulation (GRE) + +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. + +Abstract + + This document specifies a protocol for performing encapsulation of an + arbitrary network layer protocol over another arbitrary network layer + protocol. + +Introduction + + A number of different proposals [RFC 1234, RFC 1226] currently exist + for the encapsulation of one protocol over another protocol. Other + types of encapsulations [RFC 1241, SDRP, RFC 1479] have been proposed + for transporting IP over IP for policy purposes. This memo describes + a protocol which is very similar to, but is more general than, the + above proposals. In attempting to be more general, many protocol + specific nuances have been ignored. The result is that this proposal + is may be less suitable for a situation where a specific "X over Y" + encapsulation has been described. It is the attempt of this protocol + to provide a simple, general purpose mechanism which is reduces the + problem of encapsulation from its current O(n^2) problem to a more + manageable state. This proposal also attempts to provide a + lightweight encapsulation for use in policy based routing. This memo + explicitly does not address the issue of when a packet should be + encapsulated. This memo acknowledges, but does not address problems + with mutual encapsulation [RFC 1326]. + + In the most general case, a system has a packet that needs to be + encapsulated and routed. We will call this the payload packet. The + payload is first encapsulated in a GRE packet, which possibly also + includes a route. The resulting GRE packet can then be encapsulated + in some other protocol and then forwarded. We will call this outer + + + +Hanks, Li, Farinacci & Traina [Page 1] + +RFC 1701 Generic Routing Encapsulation (GRE) October 1994 + + + protocol the delivery protocol. The algorithms for processing this + packet are discussed later. + +Overall packet + + The entire encapsulated packet would then have the form: + + --------------------------------- + | | + | Delivery Header | + | | + --------------------------------- + | | + | GRE Header | + | | + --------------------------------- + | | + | Payload packet | + | | + --------------------------------- + +Packet header + + The GRE packet header 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 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + |C|R|K|S|s|Recur| Flags | Ver | Protocol Type | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Checksum (optional) | Offset (optional) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Key (optional) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Sequence Number (optional) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Routing (optional) + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Flags and version (2 octets) + + The GRE flags are encoded in the first two octets. Bit 0 is the + most significant bit, bit 15 is the least significant bit. Bits + 13 through 15 are reserved for the Version field. Bits 5 through + 12 are reserved for future use and MUST be transmitted as zero. + + + + + + +Hanks, Li, Farinacci & Traina [Page 2] + +RFC 1701 Generic Routing Encapsulation (GRE) October 1994 + + + Checksum Present (bit 0) + + If the Checksum Present bit is set to 1, then the Checksum field + is present and contains valid information. + + If either the Checksum Present bit or the Routing Present bit are + set, BOTH the Checksum and Offset fields are present in the GRE + packet. + + Routing Present (bit 1) + + If the Routing Present bit is set to 1, then it indicates that the + Offset and Routing fields are present and contain valid + information. + + If either the Checksum Present bit or the Routing Present bit are + set, BOTH the Checksum and Offset fields are present in the GRE + packet. + + 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. + + Strict Source Route (bit 4) + + The meaning of the Strict Source route bit is defined in other + documents. It is recommended that this bit only be set to 1 if + all of the the Routing Information consists of Strict Source + Routes. + + Recursion Control (bits 5-7) + + Recursion control contains a three bit unsigned integer which + contains the number of additional encapsulations which are + permissible. This SHOULD default to zero. + + Version Number (bits 13-15) + + The Version Number field MUST contain the value 0. Other values + are outside of the scope of this document. + + + +Hanks, Li, Farinacci & Traina [Page 3] + +RFC 1701 Generic Routing Encapsulation (GRE) October 1994 + + + Protocol Type (2 octets) + + The Protocol Type field contains the protocol type of the payload + packet. In general, the value will be the Ethernet protocol type + field for the packet. Currently defined protocol types are listed + below. Additional values may be defined in other documents. + + Offset (2 octets) + + The offset field indicates the octet offset from the start of the + Routing field to the first octet of the active Source Route Entry + to be examined. This field is present if the Routing Present or + the Checksum Present bit is set to 1, and contains valid + information only if the Routing Present bit is set to 1. + + Checksum (2 octets) + + The Checksum field contains the IP (one's complement) checksum of + the GRE header and the payload packet. This field is present if + the Routing Present or the Checksum Present bit is set to 1, and + contains valid information only if the Checksum Present bit is set + to 1. + + Key (4 octets) + + The Key field contains a four octet number which was inserted by + the encapsulator. It may be used by the receiver to authenticate + the source of the packet. The techniques for determining + authenticity are outside of the scope of this document. The Key + field is only present if the Key Present field is set to 1. + + Sequence Number (4 octets) + + The Sequence Number field contains an unsigned 32 bit integer + which is inserted by the encapsulator. It may be used by the + receiver to establish the order in which packets have been + transmitted from the encapsulator to the receiver. The exact + algorithms for the generation of the Sequence Number and the + semantics of their reception is outside of the scope of this + document. + + Routing (variable) + + The Routing field is optional and is present only if the Routing + Present bit is set to 1. + + + + + + +Hanks, Li, Farinacci & Traina [Page 4] + +RFC 1701 Generic Routing Encapsulation (GRE) October 1994 + + + The Routing field is a list of Source Route Entries (SREs). Each + SRE 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 | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Routing Information ... + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + The routing field is terminated with a "NULL" SRE containing an + address family of type 0x0000 and a length of 0. + + Address Family (2 octets) + + The Address Family field contains a two octet value which indicates + the syntax and semantics of the Routing Information field. The + values for this field and the corresponding syntax and semantics for + Routing Information are defined in other documents. + + SRE Offset (1 octet) + + The SRE Offset field indicates the octet offset from the start of the + Routing Information field to the first octet of the active entry in + Source Route Entry to be examined. + + SRE Length (1 octet) + + The SRE Length field contains the number of octets in the SRE. If + the SRE Length is 0, this indicates this is the last SRE in the + Routing field. + + Routing Information (variable) + + The Routing Information field contains data which may be used in + routing this packet. The exact semantics of this field is defined in + other documents. + +Forwarding of GRE packets + + Normally, a system which is forwarding delivery layer packets will + not differentiate GRE packets from other packets in any way. + However, a GRE packet may be received by a system. In this case, the + system should use some delivery-specific means to determine that this + is a GRE packet. Once this is determined, the Key, Sequence Number + and Checksum fields if they contain valid information as indicated by + the corresponding flags may be checked. If the Routing Present bit + + + +Hanks, Li, Farinacci & Traina [Page 5] + +RFC 1701 Generic Routing Encapsulation (GRE) October 1994 + + + is set to 1, then the Address Family field should be checked to + determine the semantics and use of the SRE Length, SRE Offset and + Routing Information fields. The exact semantics for processing a SRE + for each Address Family is defined in other documents. + + Once all SREs have been processed, then the source route is complete, + the GRE header should be removed, the payload's TTL MUST be + decremented (if one exists) and the payload packet should be + forwarded as a normal packet. The exact forwarding method depends on + the Protocol Type field. + +Current List of Protocol Types + + The following are currently assigned protocol types for GRE. Future + protocol types must be taken from DIX ethernet encoding. For + historical reasons, a number of other values have been used for some + protocols. The following table of values MUST be used to identify + the following protocols: + + Protocol Family PTYPE + --------------- ----- + Reserved 0000 + SNA 0004 + OSI network layer 00FE + PUP 0200 + XNS 0600 + IP 0800 + Chaos 0804 + RFC 826 ARP 0806 + Frame Relay ARP 0808 + VINES 0BAD + VINES Echo 0BAE + VINES Loopback 0BAF + DECnet (Phase IV) 6003 + Transparent Ethernet Bridging 6558 + Raw Frame Relay 6559 + Apollo Domain 8019 + Ethertalk (Appletalk) 809B + Novell IPX 8137 + RFC 1144 TCP/IP compression 876B + IP Autonomous Systems 876C + Secure Data 876D + Reserved FFFF + + See the IANA list of Ether Types for the complete list of these + values. + + URL = ftp://ftp.isi.edu/in-notes/iana/assignments/ethernet-numbers. + + + +Hanks, Li, Farinacci & Traina [Page 6] + +RFC 1701 Generic Routing Encapsulation (GRE) October 1994 + + +References + + RFC 1479 + Steenstrup, M. "Inter-Domain Policy Routing Protocol + Specification: Version 1", RFC1479, BBN Systems and Technologies, + July 1993. + + RFC 1226 + Kantor, B. "Internet Protocol Encapsulation of AX.25 Frames", RFC + 1226, University of California, San Diego, May 1991. + + RFC 1234 + Provan, D. "Tunneling IPX Traffic through IP Networks", RFC 1234, + Novell, Inc., June 1991. + + RFC 1241 + Woodburn, R., and D. Mills, "Scheme for an Internet Encapsulation + Protocol: Version 1", RFC 1241, SAIC, University of Delaware, July + 1991. + + RFC 1326 + Tsuchiya, P., "Mutual Encapsulation Considered Dangerous", RFC + 1326, Bellcore, May 1992. + + SDRP + Estrin, D., Li, T., and Y. Rekhter, "Source Demand Routing + Protocol Specification (Version 1)", Work in Progress. + + RFC 1702 + Hanks, S., Li, T., Farinacci, D., and P. Traina, "Generic Routing + Encapsulation over IPv4 networks", RFC 1702, NetSmiths, Ltd., + cisco Systems, October 1994. + +Security Considerations + + Security issues are not discussed in this memo. + + + + + + + + + + + + + + + +Hanks, Li, Farinacci & Traina [Page 7] + +RFC 1701 Generic Routing Encapsulation (GRE) October 1994 + + +Acknowledgements + + The authors would like to acknowledge Yakov Rekhter (IBM) and Deborah + Estrin (USC) for their advice, encouragement and insightful comments. + +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 + + + + + + + + + + + + + + +Hanks, Li, Farinacci & Traina [Page 8] + |