Configuring Ospf - 3Com Switch 7700 Configuration Manual

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Configuring OSPF

You must first enable OSPF then specify the interface and area ID before
configuring other functions. However, the configuration of functions that are
related to the interface does not depend on whether OSPF is enabled. However, if
OSPF is disabled, the OSPF-related interface parameters become invalid.
OSPF configuration includes tasks that are described in the following sections:
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Area
If all routers on a large network are running OSPF, the large number of routers
results in an enormous LSD, which consumes storage space, complicates the
SPF algorithm, and adds CPU load. Furthermore, as a network grows larger, the
topology becomes more likely to change. Hence, the network is always in
"turbulence", and a large number of OSFP packets are generated and
transmitted in the network. This shrinks network bandwidth. In addition, each
change causes all the routers on the network to recalculate the routes.
OSPF solves this problem by dividing an AS into different areas. Areas logically
group the routers, which form the borders of each area. Thus, some routers
may belong to different areas. A router that connects the backbone area and a
non-backbone area is called an area border router (ABR). An ABR can connect
to the backbone area physically or logically.
Backbone Area
After the area division of OSPF, one area is different from all the other areas. Its
area-id is 0 and it is usually called the backbone area.
Virtual link
Since all the areas should be connected logically, virtual link is adopted so that
the physically separated areas can still maintain logical connectivity.
Route summary
An AS is divided into different areas that are interconnected through OSPF
ABRs. The routing information between areas can be reduced by use of a route
summary. Thus, the size of routing table can be reduced and the calculation
speed of the router can be improved. After finding an intra-area route of an
area, the ABR looks in the routing table and encapsulates each OSPF route into
an LSA and sends it outside the area.
Enabling OSPF and Entering OSPF View
Entering OSPF Area View
Specifying the Interface
Configuring Router ID
Configuring the Network Type on the OSPF Interface
Configuring the Cost for Sending Packets on an Interface
Setting the Interface Priority for DR Election
Setting the Peer
Setting the Interval of Hello Packet Transmission
Setting a Dead Timer for the Neighboring Routers
Configuring an Interval Required for Sending LSU Packets
Setting an Interval for LSA Retransmission Between Neighboring Routers
OSPF 107