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426 CHAPTER 29: CONFIGURING OSPF
By default, OSPF is disabled.
Associating an Area-id
with the Specified
Interface
The OSPF protocol divides the autonomous system into areas. An area is the
logical group of the router. Some routers belong to different areas (called area
boundary router ABR), while a network segment can only be in one area. In other
words, each interface running the OSPF protocol must be put in a specific area.
The area is flagged with an area ID. The ABR transmits routing information
between areas.
In addition, in the same area, all routers must agree unanimously to the parameter
configurations of this area. So, in the configuration of routers in the same area,
most configuration data must be considered on the basis of this area. Incorrect
configurations make it impossible for adjacent routers to transfer information to
each other, or can even lead to the blocking or self-loop of routing information.
Perform the following configurations in interface view.
Table 489 Associate an Area-id with the Specified Interface which runs OSPF
No area-id is associated with the specified interface by default after OSPF is
enabled.
After OSPF is enabled, you must specify an area-id associated with the specified
interface. OSPF only works on the specified interface.
Configuring the
Network Type of the
OSPF Interface
The OSPF protocol calculates the route on the basis of the topological structure of
the neighboring network of this router. Each router describes the topology of its
neighboring network and transmits this information to all other routers.
OSPF divides the network into 4 types according to the link layer protocols:
■ When the link layer is Ethernet, OSPF regards the network type as broadcast by
default.
■ When the link layer protocol is frame relay, HDLC and X.25, OSPF regards the
network type as NBMA by default.
■ No link layer protocol is considered as point-to-multipoint type by default. It is
usually manually modified from NBMA if the NBMA network is not wholly
interconnected.
■ When the link layer protocol is PPP, LAPB, OSPF regards the network type as
point-to-point by default.
NBMA is a Non Broadcast Multi Access network. The typical network is X.25 and
frame relay. Configure the poll-interval to specify the period for sending a polling
Enable OSPF and enter into the OSPF view ospf enable
Turn off OSPF undo ospf enable
Operation Command
Specify an area-id associated with the
specified interface which runs OSPF
ospf enable area area-id
Delete an area-id associated with the
specified interface
undo ospf enable area area-id