H3C Technologies H3C S7500E Series Switches - Manual (Page 205)

6-2
z Reducing bandwidth consumption by advertising only incremental updates and therefore
applicable to advertising a great amount of routing information on the Internet
z Eliminating routing loops completely by adding AS path information to BGP routes
z Providing abundant policies to implement flexible route filtering and selection
z Good scalability
A router advertising BGP messages is called a BGP speaker. It establishes peer relationships with
other BGP speakers to exchange routing information. When a BGP speaker receives a new route or a
route better than the current one from another AS, it will advertise the route to all the other BGP peers
in the local AS.
To simplify configuration, multiple peers having an identical policy can be organized as a peer group.
BGP runs on a router in either of the following two modes:
z iBGP (internal BGP)
z eBGP (external BGP)
BGP is called iBGP when it runs within an AS and is called eBGP when it runs between ASs.
Formats of BGP Messages
Header
BGP has five types of messages:
z Open
z Update
z Notification
z Keep-alive
z Route-refresh
They have the same header, as shown below:
Figure 6-1 BGP message header
z Marker: The 16-byte field is used to delimit BGP messages. The Marker must be all ones.
z Length: The 2-byte unsigned integer indicates the total length of the message.