3.6.a Describe packet types

  • 3.6.a [i] LSA types [1, 2, 3, 4, 5, 7, 9]

LSA type 1

Router LSA:  the router advertises its presence along with the links to other routers or networks and their metrics within the same area. Type 1 LSAs are flooded only in their own area. The originating router provides the link state id for type 1 link state advertisements.

LSA type 2

Network LSA: the DR of a broadcast segment lists the routers joined by the segment. Type 2LSAs are flooded only in their own area. the link state id is the ip interface address of the DR.

LSA type 3

Summary Network LSA: originated from an ABR to advertise the subnets in an area to routers outside that area. When an ABR receives a Type1 or 2 LSA, it generates a Type 3 LSA for the networks learned from the Type 1 or 2 LSA to other areas. the link state id is the ip  address of the subnet/s being advertised.

LSA type 4

Summary ASBR LSA: similar to type 3, however, it advertises a host route used to reach the ASBR. the link state id is the RID of the ASBR. not flooded to stub areas.

LSA TYPE 5

External: as the name implies, type 5 LSA’s contain information about other routing processes being imported to OSPF. the link state id is the external network number. not flooded to stub areas.

LSA type 7

NSSA:  creates a special type of link-state advertisement, which can only exist in an NSSA area. An NSSA ASBR generates this LSA and an NSSA ABR translates it into a type 5 LSA, which gets propagated into the OSPF domain.

LSA type 9

Link-local Opaque: for OSPFv2, and  Intra-Area-Prefix LSA for OSPFv3. It is the OSPFv3 LSA that contains prefixes for stub and transit networks in the link-state ID.