As Number Migration - Dell Force10 S4810P Configuration Manual

Figure 9-10. Dynamic changes when bgp asnotation command is disabled in the show running
config
AS NOTATION DISABLED
FTOS(conf-router_bgp)#no bgp asnotation
FTOS(conf-router_bgp)#sho conf
!
router bgp 100
bgp four-octet-as-support
neighbor 172.30.1.250
<output truncated>
FTOS(conf-router_bgp)#do sho ip bgp
BGP table version is 28093,
AS4 SUPPORT DISABLED
FTOS(conf-router_bgp)#no bgp four-octet-as-support
FTOS(conf-router_bgp)#sho conf
!
router bgp 100
neighbor 172.30.1.250
FTOS(conf-router_bgp)#do show ip bgp
BGP table version is 28093,

AS Number Migration

When migrating one AS to another, perhaps combining ASs, an eBGP network may lose its routing to an
iBGP if the ASN changes. Migration can be difficult as all the iBGP and eBGP peers of the migrating
network need to be updated to maintain network reachability. With this feature you can transparently
change the AS number of entire BGP network and ensure that the routes are propagated throughout the
network while the migration is in progress. Essentially,
to operate as if it belongs to "virtual" AS network besides its physical AS network.
Figure 9-11 shows a scenario where Router A, Router B and Router C belong to AS 100, 200, 300
respectively. Router A acquired Router B; Router B has Router C as its customer. When Router B is
migrating to Router A, it needs to maintain the connection with Router C without immediately updating
Router C's configuration.
belongs to Router B's old network (AS 200) as far as communicating with Router C is concerned.
local-as 65057
local router ID is 172.30.1.57
local-as 65057
local router ID is 172.30.1.57
allows this to happen by allowing Router B to appear as if it still
Local-AS
provides a capability to the BGP speaker
Local-AS
Border Gateway Protocol | 191