Ospf Packets - H3C SecPath F1800-A Operation Manual

Operation Manual - Network and Routing Protocol
H3C SecPath F1800-A Firewall
Figure 5-1 Area and route aggregation

5.1.4 OSPF Packets

OSPF uses five types of packets:
Hello message:
It is a kind of most common packet, which is sent to the peer of a local router regularly.
It contains the values of some timers, DR, BDR and the known peer.
DD packet (Database Description Packet):
When two routers synchronize their databases, they use the DD packets to describe
their own LSDBs, including the summary of each LSA. The summary refers to the
HEAD of an LSA, which can be used to uniquely identify the LSA. This reduces the
traffic size transmitted between the routers, since the HEAD of an LSA only occupies
a small portion of the overall LSA traffic. With the HEAD, the peer router can judge
whether it already has had the LSA.
Link State Request (LSR) Packet:
After exchanging the DD packets, the two routers know which LSAs of the peer
routers are lacked in the local LSDBs. In this case, they will send LSR packets to
request for the needed LSAs to the peers. The packets contain the summary of the
needed LSAs.
Link State Update (LSU) Packet:
The packet is used to send the needed LSAs to the peer router. It contains a collection
of multiple LSAs (complete contents).
Link State Acknowledgment (LSAck) packet
The packet is used to acknowledge the received LSU packets. It contains the HEAD(s)
of LSA(s) to be acknowledged (a packet can acknowledge multiple LSAs).
Area 0
Area 8
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Chapter 5 OSPF Configuration
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Virtual Link
RTA
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Area 19