Bgp full mesh8/15/2023 Two BGP routers become neighbors after the routers establish a TCP connection between each other. The BGP neighbor formation indicates the routers that attempt to talk via BGP. These statements indicate that RTA runs BGP and belongs to AS100. Issue this command to enable BGP on a router: router bgp autonomous-system In the second example, both routers belong to the same AS.ĭefine the router process and the AS number to which the routers belong. In the first example, RTA and RTB are in different ASs. Enable BGP RoutingĬomplete these steps in order to enable and configure BGP.Īssume that you want to have two routers, RTA and RTB, talk via BGP. When BGP runs between routers in the same AS, this is called iBGP. ![]() When BGP runs between routers that belong to two different ASs, this is called exterior BGP (eBGP). ![]() Redistribution of BGP information to IGPs that run in the AS Internal BGP (iBGP) peering between routers inside an AS In order to assure network reachability, these processes take place: In order to send the information to external ASs, there must be an assurance of the reachability for networks. As the diagram in this section shows, AS200 is a transit AS for AS100 and AS300. If an AS has multiple BGP speakers, the AS can serve as a transit service for other ASs. Notification packets go out in response to errors or special conditions. The send of keepalive packets ensures that the connection between the BGP peers is alive. The version number changes whenever BGP updates the table with routing information changes. The version number is the same for all the BGP peers. BGP keeps a version number of the BGP table. After this exchange, the peers send incremental updates as the routing table changes. BGP peers initially exchange the full BGP routing tables. The graph also shows where to apply routing policies in order to enforce some restrictions on the routing behavior.Īny two routers that form a TCP connection in order to exchange BGP routing information are "peers" or "neighbors". This information helps in the construction of a graph of ASs that are loop-free. This information is mainly an indication of the full paths that a route must take in order to reach the destination network. The peer routers exchange messages to open and confirm the connection parameters.īGP routers exchange network reachability information. ![]() Two BGP routers form a TCP connection between one another. How Does BGP Work?īGP uses TCP as the transport protocol, on port 179. The routers can use an exterior gateway protocol to route packets outside the AS. ![]() Routers in an AS can use multiple Interior Gateway Protocols (IGPs) to exchange routing information inside the AS. An AS is a set of routers under a single technical administration. The BGP, which RFC 1771 defines, allows you to create loop-free interdomain routing between autonomous systems (ASs). Refer to Cisco Technical Tips Conventions for more information on document conventions. If your network is live, ensure that you understand the potential impact of any command. All of the devices used in this document started with a cleared (default) configuration. The information in this document was created from the devices in a specific lab environment. This document is not restricted to specific software and hardware versions. There are no specific requirements for this document. This document describes five Border Gateway Protocol (BGP) case studies.
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