H3C Technologies H3C S10500 Series Switches - Manual (Page 234)

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Figure 89 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
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.
Follow these steps to configure AS number substitution for a peer or peer group:
To do… Use the command… Remarks
Enter system view system-view —
Enter BGP view bgp as-number —
Replace the AS number of a peer or peer
group in the AS_PATH attribute as the local
AS number
peer { group-name | ip-address }
substitute-as Required
Not configured by default.
CAUTION:
Improper AS number substitution configuration may cause route loops; use this command with caution.
Remove private AS numbers from updates to a peer or peer group
Follow these steps to remove private AS numbers from updates to a peer or peer group:
To do… Use the command… Remarks
Enter system view system-view —
Enter BGP view bgp as-number —
Configure BGP to remove private AS
numbers from the AS_PATH attribute of
updates to a peer or peer group
peer { group-name | ip-address }
public-as-only
Required
By default, BGP updates
carry private AS numbers.
Ignore the first AS number of eBGP route updates
Typically, BGP checks the AS_PATH attribute of a route update received from a peer. If the first AS number
is not that of the BGP peer, the BGP router discards the route update.
Follow these steps to ignore the first AS number of eBGP route updates:
To do… Use the command… Remarks
Enter system view system-view —
Enter BGP view bgp as-number —