Category: OSPF

OSPF Type 5 LSA

OSPF uses the Type5 external link LSAs to advertise external routes originated from an ASBR. They are flooded through the whole OSPF domain (at least into the parts where they are accepted) and point packets for those external addresses to the ASBR. There is a field called Forward Address within that Type5 LSA, which is usually set to 0.0.0.0 which means that the packets should be sent directly to the ASBR.

Continue reading

OSPF Network Command

The OSPF network command is used to activate OSPF on the specified interfaces. Specifying an interface with the command will include the interface into the OSPF routing process. On broadcast and point-to-point network types, the router will automatically start the neighbor discovery process by sending hello packets to the AllSPFRouters multicast address (224.0.0.5) after an interface has been integrated into the OSPF process.

If there’s another OSPF router on that link and their Hello packets match, they will try to form an adjacency but that’s another story.

Continue reading