HP 6125G HP 6125G & 6125G/XG Blade Switches Layer 3 - IP Routing Confi - Page 156

Specifying a fake AS number for a peer or 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 or peer groups. In this way, these EBGP peers still think Router A is in AS 2 and need not change their configurations. This feature ensures uninterrupted BGP services. To specify a fake AS number for a peer or peer group: Step Command Remarks 1. Enter system view. system-view N/A 2. Enter BGP view. bgp as-number N/A Optional. 3. Specify a fake AS number for a peer or peer { group-name | ip-address } Not specified by default. peer group. fake-as as-number This command is only applicable to an EBGP peer or peer group. Configuring AS number substitution In MPLS L3VPN, if EBGP is used between PE and CE, sites in different geographical areas must have different AS numbers assigned to ensure correct route advertisement. If different CEs use the same AS number, you must configure the relevant PE to replace the AS number of the CE as its own AS number. This feature is used for route advertisement only. Figure 61 AS number substitution configuration 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. To configure AS number substitution for a peer or peer group: Step Command Remarks 1. Enter system view. system-view N/A 2. Enter BGP view. bgp as-number N/A Not configured by default. 3. 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 Improper AS number substitution configuration may cause route loops; use this command with caution. 146