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8.4 | ![]() |
Redistribution Example | |
8.4.2 | ![]() |
Phase 2: adding OSPF to the core of a RIP network |
A common first step in migrating a RIP
network to an OSPF network is to configure backbone routers that run
both RIP and OSPF. This is while the remaining network devices run RIP. These
backbone routers act as OSPF ASBRs. Each ASBR controls the flow of
routing information between OSPF and RIP. In Figure
![]() Because RIP does not need to run between the backbone routers, updates can be suppressed using the passive-interface command. Although the following example specifies RTA, the same commands could be entered on the other routers:
Instead of RIP updates, OSPF updates will carry the redistributed information across the WAN links. The necessary OSPF routing and redistribution commands are shown as follows:
The subnets keyword tells OSPF to redistribute all subnet routes. Without the subnets keyword, only networks that are not subnetted are redistributed by OSPF. The redistributed RIP routes appear as external Type 2 routes in OSPF, as discussed in Module 6 OSPF. Mutual redistribution must be configured for other routers in the RIP
domain, those not shown in Figure
Note that the redistribute command includes the OSPF process ID, 109. The other keywords, match internal external 1 and external 2, instruct RIP to redistribute internal OSPF routes, as well as external Type 1 and Type 2 routes. This is the default for OSPF redistribution. These keywords are required only if its behavior is to be modified. As illustrated in Figure
The following configuration allows the OSPF process on RTA to redistribute RIP information, only for networks 130.10.8.0 through 130.10.15.0:
These commands prevent RTA from advertising networks in other RIP domains onto the OSPF backbone. This prevents other boundary routers from using false information and forming a loop. When an OSPF backbone area is in place, the RIP domains can easily be converted into OSPF areas.
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