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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. When Router B is migrating to Router A, it must maintain the connection with
Router C without immediately updating Router C’s conguration. 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 22. 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.
BGP4 Management Information Base (MIB)
The FORCE10-BGP4-V2-MIB enhances Dell Networking OS BGP management information base (MIB) support with many new simple
network management protocol (SNMP) objects and notications (traps) dened in draft-ietf-idr-bgp4-mibv2-05. To see these
enhancements, download the MIB from the Dell Networking website, www.dell.com.
NOTE
: For the
Force10-BGP4-V2-MIB
and other MIB documentation, refer to the Dell iSupport web page.
Border Gateway Protocol IPv4 (BGPv4) 179