Huawei S6700 Series Configuration Manual page 104

S6700 Series Ethernet Switches
Configuration Guide - IP Routing
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Area Division
The number of switchs increases with the unceasing expansion of the network scale. This leads
to a large LSDB on each switch. As a result, the load of each switch is very heavy. OSPF solves
this problem by dividing an AS into different areas. An area is regarded as a device group
logically. Each group is identified by an area ID. On the border of an area resides a switch rather
than a link. A network segment (or a link) belongs to only one area. That is, the area to which
each OSPF interface belongs must be specified, as shown in
Figure 4-1 OSPF area division
After area division, route aggregation can be performed on border routers to reduce the number
of LSAs advertised to other areas. Route aggregation also minimizes the influence caused by
changes in the topology.
Router Type
OSPF routers are classified into the following types according to their locations in the AS:
l
l
Issue 01 (2012-03-15)
Each OSPF device collects the LSAs from other devices, and all these LSAs compose the
LSDB. An LSA describes the network topology around a switch, whereas an LSDB
describes the network topology of the whole AS.
OSPF devices transform the LSDB into a weighted directed map. The weighted directed
map reflects the topology of the entire network. All switchs in the same area have the same
map.
According to the directed map, each switch uses the Shortest Path First (SPF) algorithm to
calculate the shortest path tree, regarding itself as the root. The tree displays the routes to
each node in the AS.
Area1
Area2
Internal routers
All interfaces of the switchs of this type belong to the same OSPF area.
Area border routers (ABRs)
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Figure
Area4
Area0
Area3
4 OSPF Configuration
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