Operation Manual – Routing ProtocolH3C S7500 Series Ethernet Switches Chapter 6 BGP Configuration6-5z Data: Used to further determine the cause of errors. Its content is the error datawhich depends on the specific error code and error subcode. Its length isunfixed.V. KeepaliveIn BGP, Keepalive message keeps BGP connection alive and is exchangedperiodically. A BGP Keepalive message only contains the packet header. Noadditional field is carried.VI. Route-refreshRoute-refresh message is used to notify peers that the route refresh function isavailable.6.1.3 BGP Routing MechanismWhen BGP initially starts on a router, it sends the whole BGP routing table to its peersto exchange routing information. Afterwards, BGP sends only Update messagesinstead of the whole table. During this process, BGP also sends/receives Keepalivemessages to determine whether the connections to its peers are normal.A router running BGP is also called a BGP speaker because it can send BGPmessages. A BGP speaker can receive routing information as well as generate andadvertise routing information to other BGP speakers. When a BGP speaker receivesa route from another AS and finds this is a new route (a route it does not know) or aroute superior to any of its known routes, the BGP speaker advertises the route to allother BGP speakers in the AS.Two BGP speakers capable of exchanging BGP messages with each other are peersof each other. Multiple BGP peers can form one peer group.I. BGP route advertisement policiesIn the implementation on H3C S7500 Series Ethernet Switches (hereinafter referredto as the S7500 series), BGP adopts the following policies to advertise routes:z When there are multiple optional routes, a BGP speaker chooses only theoptimal one;z A BGP speaker advertises only the local routes to its peers;z A BGP speaker advertises the routes obtained from EBGP to all its BGP peers(including both EBGP and IBGP peers);z A BGP speaker does not advertise the routes obtained from IBGP to its IBGPpeers;z A BGP speaker advertises the routes obtained from IBGP to its EBGP peers (inthe S7500 series, BGP and IGP does not synchronize with each other);z Once a BGP speaker sets up a connection to a new peer, it advertises all its BGProutes to the new peer.
