Redistribution Problems


In this section, we will discuss the redistribution problems encountered in BGP. Consider the example depicted in Figure 11.9.

click to expand
Figure 11.9: A BGP network showing a redistribution problem.

In Figure 11.9, BGP is running between router A1 of AS5555 and router B1 of AS6666. Routers A1 and A2 have static routes configured between them. Redistribution of static routes is configured at A1. Suppose route 192.168.1.0/24 is not available in the routing table of B1 of AS6666.

To troubleshoot this problem:

  1. Check the availability of route 192.168.1.0/24 at A1 if any static route is configured. This is performed by using the show ip route command. The output of show ip route is shown in Listing 11.28.

    Listing 11.28 Output of show ip route Command at A1

    start example
    A1#show ip route 192.168.1.0 Routing entry for 192.168.1.0/24   Known via "static", distance 1, metric 0   Redistributing via bgp 5555   Routing Descriptor Blocks:   10.10.2.2       Route metric is 0, traffic share count is 1
    end example

  2. Check the presence of the network in the BGP table of A1 using the command

    A1#show ip bgp 192.168.1.0 % Network not in table

    The network is not available in the BGP table, which indicates that it is not declared in BGP.

  3. Check the redistribution, because static routes are used to advertise the networks and not the network command. The relevant part of the configuration of A1 is shown in Listing 11.29.

Listing 11.29 Configuration of A1

start example
router bgp 5555 neighbor 10.10.1.2 remote-as 6666 redistribute static route-map redis-stat ! route-map redis-stat permit 10 match ip address 15 set metric 10 ! access-list 15 permit 10.10.0.0 0.0.0.255
end example

Listing 11.29 shows that redistribution of static routes into BGP is controlled by using the route map redis-stat, which allows routes matching access list 15. Network 192.168.1.0/24 does not match access list 15 and is not redistributed.

The modified access list configuration, which would allow the route 192.168.1.0/24 to be redistributed into BGP, is as shown:

access-list 15 permit 10.10.0.0 0.0.0.255 access-list 15 permit 192.168.1. 0.0.0.255




Cisco IP Routing Protocols(c) Trouble Shooting Techniques
Cisco IP Routing Protocols: Trouble Shooting Techniques (Charles River Media Networking/Security)
ISBN: 1584503416
EAN: 2147483647
Year: 2006
Pages: 130

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