3Com S7906E Configuration Manual page 800

To do...
Enter system view
Enter BGP view
Disable BGP from considering
AS_PATH during best route selection
Specify a fake AS number for a peer/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/peer groups. In this way, these eBGP peers still think Router A is
in AS 2 and thus need not change their configurations. This feature ensures uninterrupted BGP
services.
Follow these steps to specify a fake AS number for a peer/peer group:
To do...
Enter system view
Enter BGP view
Specify a fake AS number for a
peer/peer group
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 1-19 AS number substitution configuration
EBGP_Update:10.1.1.1/32
AS_PATH:800
CE 1
AS 800
Use the command...
system-view
bgp as-number
bestroute as-path-neglect
Use the command...
system-view
bgp as-number
peer { group-name |
ip-address } fake-as
as-number
AS 100
PE 1
MPLS backbone
VPNv4_Update:10.1.0.0/16
RD:10.1.1.1/32
AS_PATH:800
1-31
—
—
Optional
By default, BGP
considers AS_PATH
during best route
selection.
—
—
Optional
Not specified by default
PE 2
EBGP_Update:10.1.1.1/32
AS_PATH:100,100
CE 2
AS 800
Remarks
Remarks