Filter OSPF prefixes inter-Area

Filter OSPF prefixes inter-Area


Suppose you have an OSPF domain consists of two areas, area 0 and 1, and you want area 1 to be a NSSA area (means no Type 3 LSA import into this area), yet you also want the area 0 has no specific route from area 1 imported into it, you can use the “Filter” command under the OSPF-Area hierarchy to achieve this requirement, topology and scripts are shown below:

Figure 1 – Topology





R1 Configuration





R2 Configuration



R3 Configuration




R4 Configuration



Before applying the prefixes filter, all prefixes from Area 1 are in the R1’s routing table:


After apply the filter, all prefixes from Area 1 were refrained from leaking into Area 0 (backbone), no route from area 1 are in R1’s routing table anymore.

Thanks for reading.

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