Dynamic routing

OSPF areas and LSA types

Also called area 0, backbone area, ABR, area border router, ASBR, LSA type, summary LSA, external LSA, type 1, type 2, type 3, type 4, type 5, E2

OSPF splits a big network into areas around area 0, with border routers summing one area up for another.

Inside an area every router shares the full map: type 1 router LSAs and type 2 network LSAs (by a DR). An ABR, in area 0 and another area, passes networks across as type 3 summary LSAs, so each area's database and SPF stay small. An ASBR brings in routes from outside OSPF (a default route, say) as type 5 external LSAs, flooded to every normal area, and ABRs add a type 4 saying how to reach the ASBR. Every area joins area 0.

See it on real machines

Learn it on real machines.