OSPF Network LSA (Type 2 LSA)

OSPF network LSAs (or type 2 LSA) are generated for NBMA (non broadcast multiaccess) and transit broadcast networks that resides in an area. As a transit broadcast network could serve an Ethernet network where two or more routers are connected via ethernet links and share the same broadcast domain like in the picture below.network-lsa

In the picture you see an OSPF network, where there is a broadcast domain, which consists of R2 with R1 and ABR connected through a ethernet switch. Unlike router LSAs, which are generated by every router, network LSAs (type 2 LSAs) are generated only by DR (Designated Router) for the multiaccess network. In current topology, ABR router, is at the same time Designated Router (because of highest router id – for ethernet segment between R1-R2-ABR, so, ABR is in charge for generating type 2 LSA to represent this multiaccess network in area 0. Let’s have a look at some output from “show ip ospf database“.


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