FIGURE 21 AS external LSA reduction
Notice that both Router D and Router E have a route to the other routing domain through Router F.
OSPF eliminates the duplicate AS External LSAs. When two or more devices are congured as ASBRs have equal-cost routes to the
same next-hop router in an external routing domain, the ASBR with the highest router ID oods the AS External LSAs for the external
domain into the OSPF AS, while the other ASBRs ush the equivalent AS External LSAs from their databases. As a result, the overall
volume of route advertisement trac within the AS is reduced and the devices that ush the duplicate AS External LSAs have more
memory for other OSPF data. Because Router D has a higher router ID than Router E, Router D oods the AS External LSAs for Router
F to Routers A, B, and C. Router E ushes the equivalent AS External LSAs from its database.
Reduction of equivalent AS external LSAs
FastIron Ethernet Switch Layer 3 Routing
228 53-1003627-04
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