Redistribution Problem

In IS-IS, L1 and L2 routers maintain a single link-state database, which stores routing information. An L1-L2 router maintains a 2-link-state database. An L1-L2 router propagates information about an L1 area to an L2 area with the help of a 2-link-state database. As a result, full routing is achieved between different IS-IS area levels. This is known as redistribution in IS-IS. Consider the scenario depicted in Figure 10.5 to understand redistribution between IS-IS and other routing protocols.

Figure 10.5: Redistribution between OSPF and IS-IS routing domains in a network.

Figure 10.5 shows part of a network that consists of an IS-IS domain and an OSPF routing domain. Routers R1 and R2 are configured in the IS-IS routing protocol and redistribute routing information to router R4, which is in the OSPF routing domain.

In Figure 10.5, incorrect redistribution configuration will result in loss of routing information, because the routing information does not reach the intended recipient properly. This is known as route leaking. To troubleshoot the redistribution problem in this network, configure R2 with the correct router redistribution configuration as shown in Listing 10.30.

Listing 10.30 Correct Router Configuration at R2

interface create ip pos3/1 address-netmask 18.1.1.1/30 port so.3.1 interface create ip fe1/1 address-netmask 14.2.2.2/24 port et.1.1 interface create ip gi2/1 address-netmask 172.148.8.2/24 port gi.2.1 interface add ip lo0 address-netmask 14.2.2.2/32 ! ip-router global set router-id 14.2.2.2 ! ospf create area 0.0.0.0 ospf add interface pos3/1 to-area 0.0.0.0 ospf start ! isis add area 49.0001 isis add interface fe1/1 isis set system-id 0000.0000.0002 isis start ! ip-router policy redistribute from-proto direct to-proto ospf ip-router policy redistribute from-proto isis-level-2 to-proto    ospf ip-router policy redistribute from-proto direct to-proto isis-   level-2 ip-router policy redistribute from-proto ospf-ase to-proto isis-   level-2 ! system set name R2

In Listing 10.30, the correct configuration for router redistribution policy is shown in bold.