Huawei Quidway NetEngine80E Configuration Manual page 977

HUAWEI NetEngine80E/40E Router
Configuration Guide - IP Routing
Cluster_List
BGP prefers the route with the shortest Cluster_List length during BGP route selection.
An RR and its clients form a cluster. In an AS, each RR is uniquely identified by a Cluster_ID.
Similar to an AS_Path, a Cluster_List is composed of a series of Cluster_IDs and is generated
by an RR. The Cluster_List records all the RRs through which a route passes.
l Before an RR reflects a route between its clients or between its clients and non-clients, the
RR adds the local Cluster_ID to the leftmost position of the Cluster_List. If a route does
not carry any Cluster_List, the RR creates one for the route.
l After the RR receives an updated route, it checks the Cluster_List of the route. If the RR
finds that its cluster ID is included in the Cluster_List, the RR discards the route. If its
cluster ID is not included in the Cluster_List, the RR adds its cluster ID to the Cluster_List
and then reflects the route.
The following example shows how Cluster_List is used in BGP route selection. In
8-26, an IBGP peer relationship is established between each two neighboring devices in AS
65001. Router B functions as a level-1 RR, and Router D is its client. Router D functions as a
level-2 RR, and Router E is its client. Router C functions as an RR, and Router E is its client.
Router E is configured to import the route 1.1.1.9/32 to BGP.
Figure 8-26 Networking diagram with Cluster_List configurations
10.1.1.1/30
10.1.3.1/30
Run the display bgp routing-table [ ip-address ] command on Router A to check the
configurations.
# Display the routing table of Router A.
Issue 02 (2014-09-30)
Cluster 2
RR2
10.1.2.1/30
10.1.1.2/30
Router B
Router A
10.1.3.2/30
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
Cluster 1
10.1.2.2/30
Router D
AS 65001
Router C
10.1.5.1/30
RR3
Cluster3
8 BGP Configuration
Figure
RR1
10.1.4.1/30
10.1.4.2/30
Router E
10.1.5.2/30
BGP Upd
952