Deployment Guide

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 recongure 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: species that local AS values are not prepended to announcements from the neighbor.
Format: IP Address: A.B.C.D.
You must use Conguring 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 rst 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
Allowing an AS Number to Appear in its Own AS Path
This command allows you to set the number of times a particular AS number can occur in the AS path.
The allow-as feature permits a BGP speaker to allow the ASN to be present for a specied number of times in the update received from
the peer, even if that ASN matches its own. The AS-PATH loop is detected if the local ASN is present more than the specied number of
times in the command.
• Allow this neighbor ID to use the AS path the specied number of times.
CONFIG-ROUTER-BGP mode
neighbor {IP address | peer-group-name} allowas-in number
• Peer Group Name: 16 characters.
194
Border Gateway Protocol IPv4 (BGPv4)