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Configuring AS number substitution
IMPORTANT:
Do not configure AS number substitution in normal circumstances. Otherwise, routing loops might occur.
To use BGP between PE and CE in MPLS L3VPN, VPN sites in different geographical areas should have
different AS numbers. Otherwise, BGP discards route updates containing the local AS number. If two CEs
connected to different PEs use the same AS number, you must configure AS number substitution on each
PE to replace the AS number in route updates originated by the remote CE as its own AS number before
advertising them to the connected CE.
Figure 59
AS number substitution configuration (in an IPv4 network)
For example, as shown in
, CE 1 and CE 2 use the same AS number 800. To implement
bidirectional communication between the two sites, configure AS number substitution on PE 2 to replace
AS 800 as AS 100 for the BGP route update originated from CE 1 before advertising it to CE 2, and
perform the same configuration on PE 1.
To configure AS number substitution for a peer or peer group (IPv4):
Step Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Enter BGP view or BGP-VPN
instance view.
•
Enter BGP view:
bgp
as-number
•
Enter BGP-VPN instance view:
a.
bgp
as-number
b.
ip vpn-instance
vpn-instance-name
N/A
3.
Configure AS number
substitution for a peer or peer
group.
peer
{
group-name
|
ip-address
}
substitute-as
By default, AS number substitution
is not configured.
To configure AS number substitution for a peer or peer group (IPv6):
Step Command
Remarks
1.
Enter system view.
system-view
N/A
