OSPF LSU(Link State Update) Packet

The OSPF LSU packet is used to advertise the LSAs requested in the LSR packet. LSU packets may also be sent when there is some kind of network change.

Figure OSPF LSU Packet

OSPF LSU Packet Format

In the OSPF header type 4, you can see that it is an LSU packet; the format of an LSU packet is as follows

Figure OSPF LSU Packet Format

Number of LSAs

Number of LSAs is the number of LSAs contained in the LSU packet.


LSAs to be advertised in LSU packets; multiple LSAs can be included and advertised in a single LSU packet. The LSA consists of LSA header and LSA data.

How the OSPF works