destination in the network as it knows. This loop-free topology is so-called the SPF
algorithm tree.
4)
Each router will establish its own routing table according to the SPF algorithm tree.
OSPF Protocol Packet Type
During the entire learning process, OSPF routing protocol uses five types of packet, all of which
are IP packets. The packets with 89 as its IP header protocol segment are OSPF ones. This
device abides by the standard RFC protocol. And we are going to introduce the packet formats
involved in the course of OSPF routing protocol running according to the definition by RFC
documentation, and attached with the images and the meaning of key segments.
1.
OSPF Header
In the course of routing learning, OSPF uses five types of packet, which have the same OSPF
header, as shown below.
Figure 10-39 OSPF Header
1)
Version:
The version number of OSPF run by this device. For instance, the OSPF run by our
IPv4 devices is of Version 2, and that run by IPv6 devices is of Version 3.
2)
Type:
The type of this packet. There are totally five types of OSPF packets, as shown in the
table below.
Type Code Packet Name
1
Hello Packet
2
Database Description Packet
3
Link State Request Packet
4
Link State Update Packet
5
Link State Acknowledgement Packet
Table 10-3 OSPF Packet Type
3)
Router ID:
ID of the router sending this packet.
4)
Area ID
：
ID of the area that the router interface sending this packet belongs to.
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