Operation Manual – Routing ProtocolH3C S7500 Series Ethernet Switches Chapter 6 BGP Configuration6-2z In BGP, multiple routing policies are available for filtering and choosing routes ina flexible way.z BGP is extendible to allow for new types of networks.In BGP, the routers that send BGP messages are known as BGP speakers. A BGPspeaker receives and generates new routing information, and advertises theinformation to other BGP speakers. When a BGP speaker receives a route from otherAS, if the route is better than the existing routes or the route is new to the BGPspeaker, the BGP speaker advertises the route to all other BGP speakers in the AS itbelongs to.A BGP speaker is known as the peer of another BGP speaker if it exchangesmessages with the latter. A group of correlated peers can form a peer group.BGP can operate on a router in one of the following forms.z IBGP (Internal BGP)z EBGP (External BGP)When BGP runs inside an AS, it is called interior BGP (IBGP); when BGP runs amongdifferent ASs, it is called exterior BGP (EBGP).6.1.2 BGP Message TypeI. Format of a BGP packet headerBGP is message-driven. There are five types of BGP packets: Open, Update,Notification, Keepalive, and Route-refresh. They share the same packet header, theformat of which is shown by Figure 6-1.Length TypeMarker150 7 23 31Figure 6-1 Packet header format of a BGP messageThe fields in a BGP packet header are described as follows.z Marker: 16 bytes in length. This filed is used for BGP authentication. When noauthentication is performed, all the bits of this field are 1.z Length: 2 bytes in length. This filed indicates the size (in bytes) of a BGP packet,with the packet header counted in.z Type: 1 byte in length. This field indicates the type of a BGP packet. Its valueranges from 1 to 5, which represent Open, Update, Notification, Keepalive, and
