Administrator Guide
Figure 24. Before and After AS Number Migration with Local-AS Enabled
When you complete your migration, and you have recongured 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 rst 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 rst. 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.
3 Prepend "65001 65002" to as-path.
Local-AS is prepended before the route-map to give an impression that update passed through a router in AS 200 before it reached Router
B.
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Border Gateway Protocol IPv4 (BGPv4)