H3C Technologies H3C S7500E Series Switches - Manual (Page 236)

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This command is only applicable to an eBGP peer or peer group.
Configure AS number substitution
In MPLS L3VPN, if eBGP is used between PE and CE, sites in different geographical areas should
have different AS numbers assigned to ensure correct route advertisement. If different CEs use the
same AS number, you need to configure the corresponding PE to replace the AS number of the CE as
its own AS number. This feature is used for route advertisement only.
Figure 6-19 AS number substitution configuration
MPLS backbone
VPNv4_Update:10.1.0.0/16
RD:10.1.1.1/32
AS_PATH:800
EBGP_Update:10.1.1.1/32
AS_PATH:100,100
PE 1 PE 2
AS 800
EBGP_Update:10.1.1.1/32
AS_PATH:800
AS 800
AS 100
CE 1 CE 2
As shown in the above figure, CE 1 and CE 2 use the same AS number of 800. If AS number
substitution for CE 2 is configured on PE 2, when PE 2 receives a BGP update sent from CE 1, it
replaces AS number 800 as its own AS number 100. Similar configuration should also be made on PE
1.
Follow these steps to configure AS number substitution for a peer/peer group:
To do… Use the command… Remarks
Enter system view system-view —
Enter BGP view bgp as-number —
Replace the AS number of a peer/peer
group in the AS_PATH attribute as the local
AS number
peer { group-name |
ip-address } substitute-as
Optional
Not configured by default.
Improper AS number substitution configuration may cause route loops; use this command with
caution.
Remove private AS numbers from updates to a peer/peer group
Follow these steps to remove private AS numbers from updates to a peer/peer group: