Google Network Working Group D. Farinacci Request for Comments: T. Hanks Enron Communications D. Meyer Cisco Systems P. Please refer to the current edition of the "Internet Official Protocol Standards" STD 1 for the standardization state and status of this protocol.
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Farinacci Request for Comments: T. Hanks Enron Communications D. Meyer Cisco Systems P. Please refer to the current edition of the "Internet Official Protocol Standards" STD 1 for the standardization state and status of this protocol. Distribution of this memo is unlimited. All Rights Reserved. Abstract This document specifies a protocol for encapsulation of an arbitrary network layer protocol over another arbitrary network layer protocol.
Introduction A number of different proposals [RFC, RFC ] currently exist for the encapsulation of one protocol over another protocol. 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 may be less suitable for a situation where a specific "X over Y" encapsulation has been described. This memo purposely does not address the issue of when a packet should be encapsulated. This memo acknowledges, but does not address problems such as mutual encapsulation [ RFC ]. Farinacci, et al. Standards Track [Page 1] RFC Generic Routing Encapsulation March In the most general case, a system has a packet that needs to be encapsulated and delivered to some destination.
We will call this the payload packet. The payload is first encapsulated in a GRE packet. The resulting GRE packet can then be encapsulated in some other protocol and then forwarded. We will call this outer protocol the delivery protocol.
The algorithms for processing this packet are discussed later. Finally this specification describes the intersection of GRE currently deployed by multiple vendors. Structure of a GRE Encapsulated Packet A GRE encapsulated packet has the form: Delivery Header GRE Header Payload packet This specification is generally concerned with the structure of the GRE header, although special consideration is given to some of the issues surrounding IPv4 payloads.
Checksum Present bit 0 If the Checksum Present bit is set to one, then the Checksum and the Reserved1 fields are present and the Checksum field contains valid information. Note that a compliant implementation MUST accept and process this field. Bits are reserved for future use. Protocol Type 2 octets The Protocol Type field contains the protocol type of the payload packet. For purposes of computing the checksum, the value of the checksum field is zero.
This field is present only if the Checksum Present bit is set to one. The Reserved1 field is present only when the Checksum field is present that is, Checksum Present bit is set to one. Care should be taken when forwarding such a packet, since if the destination address of the payload packet is the encapsulator of the packet i.
In this case, the packet MUST be discarded. There are, however, existing implementations of RFC The following sections describe correct interoperation with such implementations. RFC Compliant Receiver An implementation complying to this specification will transmit the Reserved0 field set to zero. As stated in Section 5. Route filtering will remain unchanged. However packet filtering requires either that a firewall look inside the GRE packet or that the filtering is done on the GRE tunnel endpoints.
In those environments in which this is considered to be a security issue it may be desirable to terminate the tunnel at the firewall. This can cause large packets to become fragmented within the tunnel and reassembled at the tunnel exit independent of whether the payload packet is using PMTU.
If a tunnel entry point were to use Path MTU discovery, however, that tunnel entry point would also need to relay ICMP unreachable error messages in particular the "fragmentation needed and DF set" code back to the originator of the packet, which is not a requirement in this specification.
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The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. Standards Track [Page 9] Html markup produced by rfcmarkup 1.
GRE RFC 2784 PDF
Shaktiran 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. My journey to CCIE! Please help improve this article by adding citations to reliable sources. After receiving a certain network layer protocol such as IPX packet that needs to be encapsulated and routed, the system adds a GRE header to the packet, and then encapsulates the packet into another protocol such as IP. Offset 16 bits The offset field indicates gfe octet offset from the start of the Routing field to the first octet of the active Source Route Entry to be examined.
Generic Routing Encapsulation
Category: Informational T. Farinacci P. 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 , RFC ] currently exist for the encapsulation of one protocol over another protocol.
Farinacci Request for Comments: T. Hanks Enron Communications D. Meyer Cisco Systems P. Please refer to the current edition of the "Internet Official Protocol Standards" STD 1 for the standardization state and status of this protocol. Distribution of this memo is unlimited.