OSPF LSR(Link State Request) Packet

Request LSA by OSPF LSR packet. With DD packets, OSPF router recognize LSAs that are not in its own LSDB and newer LSAs. Then, it requests these LSAs by LSR. The LSA to be requested by LSR is identified by Link State Type, Link State ID and Advertising Router.

Figure OSPF LSR Packet
Figure OSPF LSR Packet

OSPF LSR Packet Format

Type 3 of the OSPF header indicates that it is an LSR packet; the format of LSR packet is as follows

Figure OSPF LSR Packet Format
Figure OSPF LSR Packet Format

Link State Type(32bits)

Link State Type is a number that indicates the type of LSA. The following table summarizes the Link State Type values and LSA types.

Link State Type CodeLSA Type
1Router LSA
2Network LSA
3Network summary LSA
4ASBR summary LSA
5AS External LSA
7NSSA External LSA
Table Link State Type

Link State ID(32bits)

The Link State ID is contained in the LSA header, and what the Link State ID contains depends on the type of LSA. For example, for LSA type 1, the Link State ID is the router ID of the router that generated the LSA; for LSA type 2, the Link State ID is the IP address of the DR. Also, for LSA type 3, the Link State ID is the network address of another area.

Advertising Router(32 bits)

The router ID of the router that generated the LSA.

Related articles

How the OSPF works