Border Gateway Protocol (BGP)
RFC 1105
Document | Type |
RFC - Experimental
(June 1989; No errata)
Obsoleted by RFC 1163
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Authors | |||
Last updated | 2013-03-02 | ||
Stream | Legacy | ||
Formats | plain text html pdf htmlized bibtex | ||
Stream | Legacy state | (None) | |
Consensus Boilerplate | Unknown | ||
RFC Editor Note | (None) | ||
IESG | IESG state | RFC 1105 (Experimental) | |
Telechat date | |||
Responsible AD | (None) | ||
Send notices to | (None) |
Network Working Group K. Lougheed Request for Comments: 1105 cisco Systems Y. Rekhter T.J. Watson Research Center, IBM Corp. June 1989 A Border Gateway Protocol (BGP) Status of this Memo This RFC outlines a specific approach for the exchange of network reachability information between Autonomous Systems. At the time of this writing, the Border Gateway Protocol implementations exist for cisco routers as well as for the NSFNET Nodal Switching Systems. A public domain version for "gated" is currently being implemented. Distribution of this memo is unlimited. 1. Introduction The Border Gateway Protocol (BGP) is an inter-autonomous system routing protocol. It is built on experience gained with EGP as defined in RFC 904 [1] and EGP usage in the NSFNET Backbone as described in RFC 1092 [2] and RFC 1093 [3]. The primary function of a BGP speaking system is to exchange network reachability information with other BGP systems. This network reachability information includes information on the autonomous systems (AS's) that traffic must transit to reach these networks. This information is sufficient to construct a graph of AS connectivity from which routing loops may be pruned and policy decisions at an AS level may be enforced. BGP runs over a reliable transport level protocol. This eliminates the need to implement explicit update fragmentation, retransmission, acknowledgement, and sequencing. Any authentication scheme used by the transport protocol may be used in addition to BGP's own authentication mechanisms. The initial BGP implementation is based on TCP [4], however any reliable transport may be used. A message passing protocol such as VMTP [5] might be more natural for BGP. TCP will be used, however, since it is present in virtually all commercial routers and hosts. In the following descriptions the phrase "transport protocol connection" can be understood to refer to a TCP connection. BGP uses TCP port 179 for establishing its connections. Lougheed & Rekhter [Page 1] RFC 1105 BGP June 1989 2. Summary of Operation Two hosts form a transport protocol connection between one another. They exchange messages to open and confirm the connection parameters. The initial data flow is the entire BGP routing table. Incremental updates are sent as the routing tables change. Keepalive messages are sent periodically to ensure the liveness of the connection. Notification messages are sent in response to errors or special conditions. If a connection encounters an error condition, a notification message is sent and the connection is optionally closed. The hosts executing the Border Gateway Protocol need not be routers. A non-routing host could exchange routing information with routers via EGP or even an interior routing protocol. That non-routing host could then use BGP to exchange routing information with a border gateway in another autonomous system. The implications and applications of this architecture are for further study. If a particular AS has more than one BGP gateway, then all these gateways should have a consistent view of routing. A consistent view of the interior routes of the autonomous system is provided by the intra-AS routing protocol. A consistent view of the routes exterior to the AS may be provided in a variety of ways. One way is to use the BGP protocol to exchange routing information between the BGP gateways within a single AS. In this case, in order to maintain consist routing information, these gateways MUST have direct BGP sessions with each other (the BGP sessions should form a complete graph). Note that this requirement does not imply that all BGP gateways within a single AS must have direct links to each other; other methods may be used to ensure consistent routing information. 3. Message Formats This section describes message formats and actions to be taken when errors are detected while processing these messages. Messages are sent over a reliable transport protocol connection. A message is processed after it is entirely received. The maximum message size is 1024 bytes. All implementations are required to support this maximum message size. The smallest message that may be sent consists of a BGP header without a data portion, or 8 bytes. The phrase "the BGP connection is closed" means that the transport protocol connection has been closed and that all resources for that BGP connection have been deallocated. Routing table entriesShow full document text