OSPF Type-2 Network-LSA

Type-2 Network-LSAs are originated from the DR on a broadcast or multi-access network (eg: Ethernet) to list all the routers that attached to the transit network. Type-2 LSAs are flooded within the originating area only. The Link-State ID of a Type-2 Network-LSA is the physical interface IP address of the DR that connects to the network and advertises the LSA.

OSPF Type-2 Network-LSA Format

Below lists the fields in the OSPF Type-2 Network-LSA:

Field	Description
Network Mask	Indicates the subnet mask on the transit network.
Attached Router	Lists the Router IDs of all routers on the multi-access network that have established FULL adjacency with the DR and the DR itself.

Below shows the Type-2 Network-LSA originated from RT2:

RT1#sh ip ospf database network

            OSPF Router with ID (11.11.11.11) (Process ID 100)

                Net Link States (Area 0)

  Routing Bit Set on this LSA
  LS age: 91
  Options: (No TOS-capability, DC)
  LS Type: Network Links
  Link State ID: 10.10.10.2 (address of Designated Router)
  Advertising Router: 22.22.22.22
  LS Seq Number: 80000001
  Checksum: 0xA29A
  Length: 32
  Network Mask: /24
        Attached Router: 22.22.22.22
        Attached Router: 11.11.11.11

RT1#

Note: Type-2 Network-LSAs are not necessary be generated for LAN interfaces. Type-2 LSAs are generated only when necessary, which there is more than one router attached to the LAN.