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256 Chapter 15 - OSPF
OSPF Enabled
This pull-down menu sets how the interface will function on a network
utilizing OSPF.
• If On is specified, the interface will serve as an active interface on an
OSPF network. The router will establish adjacencies with other routers.
Adjacent routers exchange database information with the Designated
Router, which then floods the information to all other routers in their
area.
• If Passive is specified, the interface will not send out Hello packets and
thus will not establish any adjacencies with other routers on that network,
even if they are running OSPF.
A Passive interface will have its network advertise to other OSPF
networks. This can be used to have a non-OSPF interface’s network
advertised into OSPF. A Passive interface must also be associated with
an OSPF Area.
• If Off is specified, the interface’s network is not advertised to the router’s
other interfaces.
Area ID
This sets the area to which this interface belongs. An area is a generalization
of an IP subnetted network. It can be specified as a number between 0 and
0xFFFFFFFF, or as an IP address in dotted-decimal notation. Area 0 is the
backbone area and is the default setting.
Cost
This number specifies the priority of one particular path over another path. An
OSPF router will choose the gateway with the lowest cost to enter into its
routing table. To give preference to a path, set a lower cost on that interface.
The value can be a number between 1 and 65,535.
Router Priority
This number sets the router priority and is only used on multi-access networks
such as LANs. This establishes whether the router is eligible to become the
Designated Router for the LAN. The value for OSPF Router Priority can be
a number between 0 and 255.
v Note: At least one router on a LAN must have a priority greater than 0 in
order for OSPF to work, since there must be a Designated Router.
The Designated Router is the single router within an area which broadcasts
the Link State Advertisement for the area. A priority of 0 means that the
router is not eligible. The router with the highest priority becomes the Desig-
nated Router.