Formats Of Bgp Messages - 3Com MSR 50 Series Configuration Manual

826 C 56: BGP C
HAPTER ONFIGURATION
Formats of BGP
Messages
A router advertising BGP messages is called a BGP speaker, which exchanges new
routing information with other BGP speakers. 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 speakers in the local AS.
BGP speakers call each other peers, and several associated peers form a peer
group.
BGP runs on a router in one of the following two modes:
IBGP (Interior BGP)
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EBGP (External BGP)
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BGP is called IBGP when it runs within an AS and is called EBGP when it runs
between ASs.
Header
BGP message involves five types:
Open message
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Update message
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Notification message
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Keep-alive message
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Route-refresh message
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They have the same header, as shown below:
Figure 231 BGP message header
Length
2 bytes
Marker: The 16-octet field is used for BGP authentication calculation. If no
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authentication information is available, then the Marker must be all ones.
Length: The 2-octet unsigned integer indicates the total length of the message.
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Type: This 1-octet unsigned integer indicates the type code of the message. The
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following type codes are defined: 1-Open 2-Update 3-Notification 4-Keepalive
5-Route-refresh. The former four are defined in RFC1771, the latter one
defined in RFC2918.
16 bytes
Marker
Type
1 bytes