Border Gateway Protocol BGP is a standardized exterior gateway protocol designed to exchange routing and reachability information among autonomous systems AS on the Internet. BGP may be used for routing within an autonomous system. The Border Gateway Protocol has been in use on the Internet since RFC corrected errors, clarified ambiguities and updated the specification with common industry practices. Ideally, even if impractical, all possible links would connect to one another, like spokes in a bicycle tire.
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BGP is an inter-Autonomous System routing protocol. This network reachability information includes information on the list of Autonomous Systems that reachability information traverses. This information is sufficient for constructing a graph of AS connectivity for this reachability, from which routing loops may be pruned and, at the AS level, some policy decisions may be enforced.
BGP This version removed the concept of "up", "down", and "horizontal" relations between autonomous systems that were present in version 1. BGP-2 introduced the concept of path attributes. In addition, BGP-2 clarified parts of the protocol that were "under-specified". BGP This version redefines the previously class-based network layer reachability portion of the updates to specify prefixes of arbitrary length in order to represent multiple classful networks in a single entry.
AS Confederation. AS Confederation Identifier. RFC An externally visible autonomous system number that identifies the confederation as a whole. A group of destinations which share some common property. An alternative to full mesh IBGP. Working groups :. BGP parameters. All routes received carrying a communities attribute containing this value MUST NOT be advertised outside a BGP confederation boundary a stand-alone autonomous system that is not part of a confederation should be considered a confederation itself.
This is an advisory qualification to readvertisement of a route prefix, permitting an AS not to readvertise the route prefix to all external bilateral peer neighbour AS's. It is consistent with these semantics that an AS may filter received prefixes that are received across a peering session that the receiver regards as a bilateral peer sessions.
IETF RFC 4271
Border Gateway Protocol (BGP) Parameters