Bgp Message Type - H3C S7500 Series Operation Manual

Operation Manual – Routing Protocol
H3C S7500 Series Ethernet Switches
In BGP, multiple routing policies are available for filtering and choosing routes in
a flexible way.
BGP is extendible to allow for new types of networks.
In BGP, the routers that send BGP messages are known as BGP speakers. A BGP
speaker receives and generates new routing information, and advertises the
information to other BGP speakers. When a BGP speaker receives a route from other
AS, if the route is better than the existing routes or the route is new to the BGP
speaker, the BGP speaker advertises the route to all other BGP speakers in the AS it
belongs to.
A BGP speaker is known as the peer of another BGP speaker if it exchanges
messages 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.
IBGP (Internal BGP)
EBGP (External BGP)
When BGP runs inside an AS, it is called interior BGP (IBGP); when BGP runs among
different ASs, it is called exterior BGP (EBGP).

6.1.2 BGP Message Type

I. Format of a BGP packet header
BGP is message-driven. There are five types of BGP packets: Open, Update,
Notification, Keepalive, and Route-refresh. They share the same packet header, the
format of which is shown by
0
Figure 6-1 Packet header format of a BGP message
The fields in a BGP packet header are described as follows.
Marker: 16 bytes in length. This filed is used for BGP authentication. When no
authentication is performed, all the bits of this field are 1.
Length: 2 bytes in length. This filed indicates the size (in bytes) of a BGP packet,
with the packet header counted in.
Type: 1 byte in length. This field indicates the type of a BGP packet. Its value
ranges from 1 to 5, which represent Open, Update, Notification, Keepalive, and
Figure 6-1.
7
Marker
Length
6-2
Chapter 6 BGP Configuration
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Type
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