Ospf Area Partition And Route Summarization - H3C S5600 Series Operation Manual

Operation Manual – Routing Protocol
H3C S5600 Series Ethernet Switches

4.1.4 OSPF Area Partition and Route Summarization

I. Area partition
If all the routers on an ever-growing large network run OSPF, the large number of
routers will result in an enormous LSDB, which will consume an enormous storage
space, complicate the running of SPF algorithm, and increase CPU load.
Furthermore, as a network grows larger, it is more likely to have changes in the
network topology. Hence, the network will often be "flapping", and a great number of
OSPF packets will be generated and transmitted in the network. This will lower the
network bandwidth utilization. Even worse, any change of the topology will cause all
the routers on the network to re-perform route calculation.
OSPF solves the above-mentioned problem by dividing an AS into multiple areas.
Areas refer to groups into which routers are logically divided. Each group is identified
by an Area ID, as shown in
Figure 4-1 OSPF area partition
On the border of an area is a router, which belongs to different areas. After area
partition, area border routers perform route summarization to reduce the number of
LSAs advertised to other areas and minimize the effect of topology changes.
II. Classification of routers
The OSPF router falls into four types according to the position in the AS:
1) Internal router
All interfaces on an internal router belong to one OSPF area.
Figure 4-1.
4-5
Chapter 4 OSPF Configuration