Ospf Configuration - 3Com 7700 Configuration Manual

78 C 5: R P
HAPTER OUTING

OSPF Configuration

O
ROTOCOL PERATION
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 the 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
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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
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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
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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.
In various configurations, you must first enable OSPF, specify the interface and
area ID before configuring other functions. But the configuration of the functions
related to the interface is not restricted by whether the OSPF is enabled or not. It
should be noted that after OSPF is disabled, the OSPF-related interface parameters
also become invalid.
OSPF configuration includes the tasks that are described in the following sections:
Enable OSPF and Enter OSPF View
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Enter OSPF Area View
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Specify Interface
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Configure Router ID
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Configure the Network Type on the OSPF Interface
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Configure the Cost for Sending Packets on an Interface
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Set the Interface Priority for DR Election
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Set the Peer
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Set the Interval of Hello Packet Transmission
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Set a Dead Timer for the Neighboring Routers
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Configure an Interval Required for Sending LSU Packets
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Set an Interval for LSA Retransmission Between Neighboring Routers
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Set a Shortest Path First (SPF) Calculation Interval for OSPF
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Configure the OSPF STUB Area
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