Operation Manual – Routing Protocol
Quidway S5600 Series Ethernet Switches-Release 1510 Chapter 5 BGP Configuration
Huawei Technologies Proprietary
5-9
RouterC
RouterD
> D=8.0.0.0
Next_Hop=3.1.1.1
Local_Pref=200
AS20
RouterB
RouterA
AS10
8.0.0.0
D=8.0.0.0
Next_Hop=2.1.1.1
Local_Pref=100
EBGP
EBGP
IBGP
IBGP
IBGP
Local_Pref=100
Local_Pref=200
2.1.1.1
3.1.1.1
Figure 5-8 Local_Pref attribute
6) Community
The Community attribute is used to simplify routing policy application and ease the
maintenance and management of routing policy. Community is a set of destination
addresses with the same features. It is not restricted to physical boundary and is
independent of AS. The Community attribute can be one of the following.
z Internet. By default, the value of the Community attributes of all routes is Internet.
That is, all routes belong to the Internet community by default. Routes with this
attribute can be advertised to all BGP peers.
z No_Export. Routes with this attribute cannot be sent to routers outside the local
AS. With the presence of the confederation, routes of this kind cannot be
advertised outside the confederation, they can only be advertised in the sub-ASs
in the confederation. (For information about confederation, refer to section
5.1.4
"
Problems in Large-Scale BGP Network”.)
z No_Advertise. Routes with this attribute cannot be advertised to any other BGP
peers after being received by a BGP router.
z No_Export_Subconfed. Routes with this attribute can neither be advertised
outside the local AS nor be advertised to other sub-ASs inside the confederation
after being received.
5.1.3 BGP Routing Policy
I. BGP routing policy
In VRP implementations, a BGP router filters routes in the following order.
z Drops the Next_Hop unreachable route.
z With Prefered-value specified, chooses the route with highest Prefered-value
value.
z Prefers the route with highest Local_Pref value.
z Prefers the routes starting from the local router.
z Prefers the route with the shortest AS path.
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