254
a. bgp as-number
[ instance
instance-name ]
b. ip vpn-instance
3. Advertise a fake AS number
to a peer or peer group.
peer
{ group-name | ipv6-address
[ prefix-length ] }
fake-as
as-number
By default, no fake AS number is
advertised to a peer or peer
group.
This command applies only to
EBGP peers or EBGP peer
groups.
Configuring AS number substitution
not configure AS number substitution in normal circumstances. Otherwise, routing loops might
To use EBGP 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. This substitution can 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 63 AS number substitution configuration (in an IPv4 network)
As shown in Figure 63, CE 1 and CE 2 use the same AS number 800. To ensure bidirectional
communication between the two sites, configure AS number substitution on PE 2. PE 2 replaces AS
800 with AS 100 for the BGP route update originated from CE 1 before advertising it to CE 2. Perform
the same configuration on PE 1.
To configure AS number substitution for a peer or peer group (IPv4 unicast/multicast address family):
1. Enter system view.
system-view
N/A
2. Enter BGP instance view or
BGP-VPN instance view.
• Enter BGP instance view:
bgp as-number [ instance
instance-name ]
• Enter BGP-VPN instance
view:
a. bgp as-number
[ instance
instance-name ]
N/A
MPLS backbone
VPNv4_Update: 10.1.0.0/16
RD: 100:1
AS_PATH: 800
EBGP_Update: 10.1.0.0/16
AS_PATH: 100, 100
PE 1 PE 2
AS 800
EBGP_Update: 10.1.0.0/16
AS_PATH: 800
AS 800
AS 100
CE 1
CE 2
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