You can configure OSPF attributes for either a
single OSPF network by using the address commands, or for all OSPF networks on a particular media interface
by using the ip ospf commands.
The size of the OSPF maximum transmission unit
(MTU) is negotiated rather than configured. OSPF database description
exchange uses the interface MTU to signal the largest OSPF MTU that
can be sent over an OSPF interface without fragmentation.
Configuring OSPF attributes for OSPF networks includes
setting the following:
Cost
Dead interval
Hello interval
Router priority
Retransmit interval
Transmit delay
Note:
Before using the address or ip ospf commands, see Precedence of Commands for information about the relationship between these commands.
address Commands
You can use the address area command to create a new OSPF interface. Use the other address commands to configure parameters for OSPF interfaces
that already exist.
The address commands
configure OSPF attributes for a single OSPF network. The ip ospf commands configure OSPF attributes for all
OSPF networks in the given interface context—for example, in
a multinet environment where multiple IP networks sit on top of an
Ethernet interface.
Note:
You must first issue the address area command before issuing any other address command.
address area
Use to create a new OSPF interface and configure the area
ID.
The interface can have an IP address, or it can be unnumbered.
Example
host1(config-router)#address 10.12.10.2 area
3
You must first issue the address area command before issuing any other address commands.
Use the no version to delete
the area ID from the specified interface.
Use to specify the time period for the router’s
neighbors to wait without seeing hello packets from the router before
they declare the router to be down.
The dead interval can be in the range 0–2147483647
seconds, and is advertised by the router’s hello packets.
For the OSPF routers to become adjacent, the dead interval
must be identical on each router.
The interface can have an IP address, or it can be unnumbered.
Use to disable the transmission of routing updates on
the interface, meaning that OSPF routing information is neither sent
by nor received through the interface.
The interface can have an IP address, or it can be unnumbered.
Example
host1(config-router)#address 192.168.100.20
area 5
The ip ospf commands
have two effects on interface configuration. These effects apply to
all ip ospf commands:
Configuration per logical IP interface (for example, Fast
Ethernet 0/1.3 or ATM 5/0.1):
The ip ospf command
configures the specified OSPF parameters for all networks configured
on the given IP interface—for example, all multinetted addresses
on an interface.
The no version of the
command resets the specified parameters to unspecified.
If the no version of
the command takes effect for a specified IP interface, there is no
default value for the specified parameters. The parameter is set back
to unspecified values. However, the value of the specified parameter
for the OSPF interface is set back to the default value or the value
previously specified by the address command.
Note:
The ip ospf commands configure OSPF
attributes for all OSPF networks in the given interface context—for
example, in a multinet environment where multiple IP networks sit
on top of an Ethernet interface. The address commands configure OSPF attributes for a single OSPF interface.
Configuration per OSPF interface:
The ip ospf command
configures the specified OSPF parameters for each OSPF interface that
sits on top of the IP interface.
The no version of the
command restores the specified parameters to the default values.
Note:
We recommend using address commands
to set attributes of OSPF interfaces created using the address area command.
ipv6 ospf area
Use to create an OSPFv3 interface under the specified
area ID or move the OSPFv3 interface from its current area to the
specified area.
Specify an optional process ID in the range 1–65535.
Example
host1(config)#interface fastethernet 0/0
host1(config-if)#ipv6 ospf area 50
Use the no version to remove
this interface from the specified area.
Use to specify that the interface disregard the MTU size
contained in the data description packet.
When enabled, the interface accepts data description packets
from its neighbor even if it has a different MTU size (the MTU size
must be less than 18000).
Specify an optional process ID in the range 1–65535.
Example
host1(config-if)#ipv6 ospf mtu-ignore
Use the no version to reset
the default: that the neighbor MTU size must match the MTU size of
the OSPFv3 interface from which the packet is received.
host1(config-router)#network 1.1.1.0 0.0.0.255
area 0
host1(config-router)#network 2.2.2.0 0.0.0.255
area 0
If you want to specify the cost, you can do so
for both interfaces simultaneously.
host1(config)#interface fastEthernet 0/0
host1(config-if)#ip ospf cost 30
You can use address commands
to create a third OSPF interface over the Ethernet interface. When
you specify a cost, you set it for only that interface.
For a single OSPF interface, when you modify the
same OSPF attribute by issuing both the ip ospf command and the address command, the
value configured with the address command
takes precedence. In other words, the most specific command for a
single OSPF interface takes precedence.
Consider the following example. Suppose you have
a numbered IP interface with an IP address of 10.10.1.1/24 sitting
on top of Fast Ethernet interface 0/0. Configure a single OSPF interface
on top of the IP interface.
host1(config)#router ospf 100
host1(router-config)#address 10.10.1.1 area
0
The default cost for this OSPF interface is 10.
Change the cost for this OSPF interface by using the address cost command.
host1(router-config)#address 10.10.1.1 cost
45
The cost for OSPF interface 10.10.1.1 is now 45.
Now use the ip ospf cost command to change the cost for this OSPF interface.
host1(config)#int fastEthernet 0/0
host1(config-if)#ip ospf cost 23
The cost of OSPF interface 10.10.1.1 does not change. The previously issued address
cost command is more specific for the interface and
takes precedence over the ip ospf cost command.
You must use the address cost command if
you want to change the cost again.
