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Maintaining Existing AS Numbers During an AS Migration
The local-as feature smooths out the BGP network migration operation and allows you to maintain
existing ASNs during a BGP network migration.
When you complete your migration, be sure to reconfigure your routers with the new information and
disable this feature.
• Allow external routes from this neighbor.
CONFIG-ROUTERBGP mode
neighbor {IP address | peer-group-name local-as as number [no prepend]
– Peer Group Name: 16 characters.
– AS-number: 0 to 65535 (2-Byte) or 1 to 4294967295 (4-Byte) or 0.1 to 65535.65535 (Dotted
format).
– No Prepend: specifies that local AS values are not prepended to announcements from the
neighbor.
Format: IP Address: A.B.C.D.
You must Configure Peer Groups before assigning it to an AS. This feature is not supported on passive
peer groups.
Example of the Verifying that Local AS Numbering is Disabled
The first line in bold shows the actual AS number. The second two lines in bold show the local AS number
(6500) maintained during migration.
To disable this feature, use the no neighbor local-as command in CONFIGURATION ROUTER BGP
mode.
R2(conf-router_bgp)#show conf
!
router bgp 65123
bgp router-id 192.168.10.2
network 10.10.21.0/24
network 10.10.32.0/24
network 100.10.92.0/24
network 192.168.10.0/24
bgp four-octet-as-support
neighbor 10.10.21.1 remote-as 65123
neighbor 10.10.21.1 filter-list Laura in
neighbor 10.10.21.1 no shutdown
neighbor 10.10.32.3 remote-as 65123
neighbor 10.10.32.3 no shutdown
neighbor 100.10.92.9 remote-as 65192
neighbor 100.10.92.9 local-as 6500
neighbor 100.10.92.9 no shutdown
neighbor 192.168.10.1 remote-as 65123
neighbor 192.168.10.1 update-source Loopback 0
neighbor 192.168.10.1 no shutdown
neighbor 192.168.12.2 remote-as 65123
neighbor 192.168.12.2 update-source Loopback 0
neighbor 192.168.12.2 no shutdown
R2(conf-router_bgp)#
Border Gateway Protocol IPv4 (BGPv4)
179