3com S7906E Manuel De Montage

 

1-31 

Enter system view 

— 

Enter BGP view 

bgp as-number 

— 

Disable BGP from considering 
AS_PATH during best route selection 

Optional 

By default, BGP 
considers AS_PATH 
during best route 
selection. 

 

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: 

Enter system view 

— 

Enter BGP view 

bgp as-number 

— 

Specify a fake AS number for a 
peer/peer group 

peer { group-name | 
ip-address } fake-as 
as-number 

Optional 

Not specified by default 

 

This command is only applicable to an eBGP peer or peer group. 

 

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 

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