SmartSwitch Router User Reference Manual 81Chapter 6: BGP Configuration GuideThe gated.conf file for router SSR2 is as follows:IBGP Configuration ExampleConnections between BGP speakers within the same AS are referred to as internal links. Apeer in the same AS is an internal peer. Internal BGP is commonly abbreviated IBGP;external BGP is EBGP.An AS that has two or more EBGP peers is referred to as a multihomed AS. A multihomedAS can “transit” traffic between two ASs by advertising to one AS routes that it learnedfrom the other AS. To successfully provide transit services, all EBGP speakers in thetransit AS must have a consistent view of all of the routes reachable through their AS.Multihomed transit ASs can use IBGP between EBGP-speaking routers in the AS tosynchronize their routing tables. IBGP requires a full-mesh configuration; all EBGPspeaking routers must have an IBGP peering session with every other EBGP speakingrouter in the AS.An IGP, like OSPF, could possibly be used instead of IBGP to exchange routinginformation between EBGP speakers within an AS. However, injecting full Internet routes(50,000+ routes) into an IGP puts an expensive burden on the IGP routers. Additionally,IGPs cannot communicate all of the BGP attributes for a given route. It is thereforerecommended that an IGP not be used to propagate full Internet routes between EBGPspeakers. IBGP should be used instead.IBGP Routing Group ExampleAn IBGP Routing group uses the routes of an interior protocol to resolve forwardingaddresses. An IBGP Routing group will determine the immediate next hops for routes byusing the next hop received with a route from a peer as a forwarding address, and usingthis to look up an immediate next hop in an IGP’s routes. Such groups support distantpeers, but need to be informed of the IGP whose routes they are using to determineimmediate next hops. This implementation comes closest to the IBGP implementation ofother router vendors.You should use the IBGP Routing group as the mechanism to configure the SSR for IBGP.If the peers are directly connected, then IBGP using group-type Internal can also be used.autonomoussystem 2 ;routerid 10.0.0.2 ;bgp yes {group type external peeras 1{peer 10.0.0.1;};};
