Operation Manual – Routing Protocol
Quidway S5600 Series Ethernet Switches-Release 1510 Chapter 5 BGP Configuration
Huawei Technologies Proprietary
5-2
z In BGP, multiple routing policies are available for filtering and choosing routes in a
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 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.
z IBGP (Internal BGP)
z 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).
5.1.1 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
Figure 5-1.
Mar ker
Length Type
0 7 15 31
Figure 5-1 Packet header format of BGP messages
The fields in a BGP packet header are described as follows.
z 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.
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 value
ranges from 1 to 5, which represent Open, Update, Notification, Keepalive, and
Route-refresh packets. Among these types of BGP packets, the first four are
defined in RFC1771, and the rest one is defined in RFC2918.
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