HP 6125G Configuration Manual page 156

Specifying a fake AS number for a peer or peer group
When Router A in AS 2 is moved to AS 3, you can configure Router A to specify a fake AS number of 2
for created connections to EBGP peers or peer groups. In this way, these EBGP peers still think Router A
is in AS 2 and need not change their configurations. This feature ensures uninterrupted BGP services.
To specify a fake AS number for a peer or peer group:
Step
1. Enter system view.
2. Enter BGP view.
3. Specify a fake AS number for a peer or
peer group.
Configuring AS number substitution
In MPLS L3VPN, if EBGP is used between PE and CE, sites in different geographical areas must have
different AS numbers assigned to ensure correct route advertisement. If different CEs use the same AS
number, you must configure the relevant PE to replace the AS number of the CE as its own AS number.
This feature is used for route advertisement only.
Figure 61 AS number substitution configuration
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, and PE 2 receives a BGP update sent from CE 1, PE 2 replaces AS number
800 as its own AS number 100. Similar configuration must also be made on PE 1.
To configure AS number substitution for a peer or peer group:
Step
1. Enter system view.
2. Enter BGP view.
3. Replace the AS number of a peer or
peer group in the AS_PATH attribute as
the local AS number.
Command
system-view
bgp as-number
peer { group-name | ip-address }
fake-as as-number
Command
system-view
bgp as-number
peer { group-name | ip-address }
substitute-as
146
Remarks
N/A
N/A
Optional.
Not specified by default.
This command is only
applicable to an EBGP peer
or peer group.
Remarks
N/A
N/A
Not configured by default.
Improper AS number
substitution configuration
may cause route loops; use
this command with caution.