The action could be to drop the route, or it could be to modify some attributes of the route before inserting it in the routing table.ĭuring the peering handshake, when OPEN messages are exchanged, BGP speakers can negotiate optional capabilities of the session, including multiprotocol extensions and various recovery modes. Each rule describes, for routes matching some given criteria, what action should be taken. This mechanism consists of a set of rules. How routes are propagated can be controlled in detail via the route-maps mechanism. These route-propagation rules effectively require that all iBGP peers inside an AS are interconnected in a full mesh with iBGP sessions. New routes learned from an iBGP peer are re-advertised to all eBGP peers only.New routes learned from an eBGP peer are re-advertised to all iBGP and eBGP peers.The main difference between iBGP and eBGP peering is in the way routes that were received from one peer are typically propagated by default to other peers: Other deployment topologies are also possible, such as running eBGP peering inside a VPN tunnel, allowing two remote sites to exchange routing information in a secure and isolated manner. Routers on the boundary of one AS exchanging information with another AS are called border or edge routers or simply eBGP peers and are typically connected directly, while iBGP peers can be interconnected through other intermediate routers. When it runs between different autonomous systems, it is called External BGP ( eBGP or Exterior Border Gateway Protocol). When BGP runs between two peers in the same autonomous system (AS), it is referred to as Internal BGP ( iBGP or Interior Border Gateway Protocol). Among routing protocols, BGP is unique in using TCP as its transport protocol. A BGP speaker sends 19-byte keep-alive messages every 30 seconds (protocol default value, tunable) to maintain the connection. It is also called the Multiprotocol Extensions which is Multiprotocol BGP (MP-BGP).īGP neighbors, called peers, are established by manual configuration among routers to create a TCP session on port 179. The new RFC allows BGP4 to carry a wide range of IPv4 and IPv6 "address families". The major enhancement was the support for Classless Inter-Domain Routing (CIDR) and use of route aggregation to decrease the size of routing tables. RFC 4271 corrected errors, clarified ambiguities and updated the specification with common industry practices. The current version of BGP is version 4 (BGP4), which was published as RFC 4271 in 2006. ![]() ![]() IPv6 BGP was first defined in RFC 1654 in 1994, and it was improved to RFC 2283 in 1998. It was first described in 1989 in RFC 1105, and has been in use on the Internet since 1994. The Border Gateway Protocol was sketched out in 1989 by engineers on the back of "three ketchup-stained napkins", and is still known as the three-napkin protocol. In contrast, the Internet application of the protocol is called Exterior Border Gateway Protocol, External BGP ( eBGP). BGP is classified as a path-vector routing protocol, and it makes routing decisions based on paths, network policies, or rule-sets configured by a network administrator.īGP used for routing within an autonomous system is called Interior Border Gateway Protocol, Internal BGP ( iBGP). ![]() ![]() Border Gateway Protocol ( BGP) is a standardized exterior gateway protocol designed to exchange routing and reachability information among autonomous systems (AS) on the Internet.
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