Brocade Virtual ADX Switch and Router Guide (Supporting ADX v03.1.00) - Manual (Page 219)

Brocade Virtual ADX Switch and Router Guide 205
53-1003246-01
Implementation of BGP4
8
In the example shown in Figure 27 , ISP-A has purchased ISP-B. The AS associated with ISP-B
changes to AS 100. If Customer C cannot or does not want to change their configuration or peering
relationship with ISP-B, a peer with Local-AS configured with the value 200 can be established on
ISP-B.
FIGURE 27 Example of Local AS configured on ISP-B
A Local AS is configured using the BGP4 neighbor command, as described in “Configuring BGP4
neighbors” on page 228. To confirm that a Local AS has been configured use the show ip BGP4
neighbor command, as described in “Displaying BGP4 neighbor information” on page 284.
BGP4 null0 routing
BGP4 considers the null0 route in the routing table (for example, static route) as a valid route, and
can use the null0 route to resolve the next hop. If the next hop for BGP4 resolves into a null0 route,
the BGP4 route is also installed as a null0 route in the routing table.
The null0 routing feature allows network administrators to block certain network prefixes using
null0 routes and route-maps, directing a remote device to drop all traffic for a network prefix by
redistributing a null0 route into BGP4.