BGP Border Gateway Protocol

Source: Internet
Author: User

BGPBorderGatewayProtocol) is the Border Gateway Protocol used to connect to independent systems on the Internet. It is an enhanced, comprehensive, and scalable protocol developed by the Internet Engineering Task Group. BGP4 supports the CIDR addressing scheme, which increases the number of available IP addresses on the Internet. BGP was designed to replace the original external gateway protocol EGP and is also considered a path vector protocol.


A route consists of two basic actions: determining the optimal path and the information group is usually called a group. The Network Transmission Group is relatively simple, and the path determination is complex. BGP is a protocol for Path Selection in today's networks. The following describes the basic operations of BGP and describes its Protocol components.

BGP implements Inter-Domain Routing in TCP/IP networks. BGP is an external Gateway Protocol (EGP), that is, it performs routing between multiple autonomous systems or domains, and exchanges routing and accessibility information with other BGP systems.

The BGP design is used to replace its predecessor with the external gateway protocol EGP) as the standard external Gateway Routing Protocol for the global Internet. BGP solves serious problems of EGP and can adapt to the rapid development of the Internet more effectively.

BGP rules in multiple RFC: RFC1771-describes BGP4, that is, the current version of BGP. RFC1654-describes the first BGP4 specification. RFC1105, RFC1163, and RFC1267-Describe the BGP version before BGP4.


BGP performs three types of routes: AS route, AS internal route, and AS route.

AS routes occur between two or more BGP routers of different AS. Peer routers of these systems use BGP to maintain a consistent network topology view, the BGP peers for AS communication must be in the same physical network. The Internet is an instance that uses this route because it consists of multiple AS or management domains. Many domains are the research institutes, companies, and entities that constitute the internet. BGP is often used for routing selection to provide the optimal path for the Internet.

AS internal routes occur between two or more BGP routers in the same AS. Peer routers in the same AS use BGP to maintain a consistent system topology view. BGP is also used to determine which router acts AS the external AS connection point. I reiterate that the Internet provides AS-based routing instances. An organization, such AS a university, can use BGP to provide optimal routing in its own management domain or. The BGP protocol can provide both AS and AS internal routes.

The pass-through (bgp) AS route occurs between two or more BGP peer routers that exchange data through the AS without running BGP. In the AS environment, BGP communication does not come from nodes in the AS and the target nodes are not in the, BGP must interact with the routing protocol used in the AS to successfully transmit BGP communication through the AS, AS shown in the AS environment:


Like other routing protocols, BGP maintains the route table, sends route update information, and determines the route based on the routing metric. The main function of the BGP system is to exchange network accessibility information of other BGP systems, including the list of AS paths. This information can be used to establish an AS system connection diagram to eliminate routing loops, and determine the execution of the AS policy.

Each BGP router maintains a route table consisting of all available paths of a specific network, but it does not clear the route table. It maintains the route information received from the peer router until it receives value-added (incremental) updates.

BGP devices exchange route information after initial data exchange and value-added update. When the router is connected to the network for the first time, the BGP router switches their entire BGP Route table. Similarly, when the route table changes, the router sends the changed part in the route table. The BGP Router does not send route updates cyclically, And the BGP Route update only contains the optimal path to a network.

BGP uses a single routing metric to determine the optimal path to a given network. This metric contains any unit value that specifies the link priority. The BGP metric is usually assigned to each link by the network administrator. The value assigned to a link can be based on any number of scales, including the number of AS passing through, stability, speed, latency, or cost.

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