neighbor 172.30.1.250 local-as 65057 truncated>Dell(conf-router_bgp)#do show ip bgpBGP table version is 31571, local router ID is 172.30.1.57 truncated>AS-PLAINDell(conf-router_bgp)#bgp asnotation asplainDell(conf-router_bgp)#sho conf!router bgp 100bgp four-octet-as-supportneighbor 172.30.1.250 local-as 65057Dell(conf-router_bgp)#do sho ip bgpBGP table version is 34558, local router ID is 172.30.1.57 truncated>Example of the Running Configuration When AS Notation is DisabledAS NOTATION DISABLEDDell(conf-router_bgp)#no bgp asnotationDell(conf-router_bgp)#sho conf!router bgp 100bgp four-octet-as-supportneighbor 172.30.1.250 local-as 65057 truncated>Dell(conf-router_bgp)#do sho ip bgpBGP table version is 28093, local router ID is 172.30.1.57AS4 SUPPORT DISABLEDDell(conf-router_bgp)#no bgp four-octet-as-supportDell(conf-router_bgp)#sho conf!router bgp 100neighbor 172.30.1.250 local-as 65057Dell(conf-router_bgp)#do show ip bgpBGP table version is 28093, local router ID is 172.30.1.57AS Number MigrationWith this feature you can transparently change the AS number of an entire BGP network and ensure thatthe routes are propagated throughout the network while the migration is in progress.When migrating one AS to another, perhaps combining ASs, an eBGP network may lose its routing to aniBGP if the ASN changes. Migration can be difficult as all the iBGP and eBGP peers of the migratingnetwork must be updated to maintain network reachability. Essentially, Local-AS provides a capability tothe BGP speaker to operate as if it belongs to "virtual" AS network besides its physical AS network.The following illustration shows a scenario where Router A, Router B, and Router C belong to AS 100,200, and 300, respectively. Router A acquired Router B; Router B has Router C as its customer. WhenRouter B is migrating to Router A, it must maintain the connection with Router C without immediatelyupdating Router C’s configuration. Local-AS allows this behavior to happen by allowing Router B toappear as if it still belongs to Router B’s old network (AS 200) as far as communicating with Router C isconcerned.Border Gateway Protocol IPv4 (BGPv4) 171
