Dell C9000 Series Networking Configuration Manual page 207

C's configuration. Local-AS allows this behavior to happen by allowing Router B to appear as if it still belongs
to Router B's old network (AS 200) as far as communicating with Router C is concerned.
Figure 24. Before and After AS Number Migration with Local-AS Enabled
When you complete your migration, and you have reconfigured your network with the new information,
disable this feature.
If you use the "no prepend" option, the Local-AS does not prepend to the updates received from the eBGP
peer. If you do not select "no prepend" (the default), the Local-AS is added to the first AS segment in the AS-
PATH. If an inbound route-map is used to prepend the as-path to the update from the peer, the Local-AS is
added first. For example, consider the topology described in the previous illustration. If Router B has an
inbound route-map applied on Router C to prepend "65001 65002" to the as-path, the following events take
place on Router B:
1 Receive and validate the update.
2 Prepend local-as 200 to as-path.
Border Gateway Protocol IPv4 (BGPv4) 207