TCP/IP Tutorial and Technical Overview - IBM Redbooks

All OSPF packets share the common header shown in Figure 5-17. The header
provides general information including area identifier, RID, checksum, and
authentication information.
Number of Octets
Figure 5-17 OSPF common header
The type field identifies the OSPF packet as one of five possible types:
Hello This packet type discovers and maintains neighbor
relationships.
Database description This packet type describes the set of LSAs contained
in the router's link state database.
Link state request This packet type requests a more current instance of
an LSA from a neighbor.
Link state update This packet type provides a more current instance of
an LSA to a neighbor.
Link state acknowledgement
This packet type acknowledges receipt of a newly
received LSA.
We describe the use of these packets in the next section.
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Version
Packet Type
Packet Length
Router ID
Area ID
Checksum
Authentication Type
Authentication Data
Version = 2
{
1= Hello
2=Database Description
3=Link State Request
4=Link State Update
5=Link State Acknowledgement
{
0=No Authentication
1=Simple Password
Password if Type 1 Selected