The example shows an OSPF area border router, Device A, that is cut o from the backbone area (area 0). To provide backbone access
to Device A, you can add a virtual link between Device A and Device C using area 1 as a transit area. To congure the virtual link, you
dene the link on the router that is at each end of the link. No conguration for the virtual link is required on the routers in the transit area.
To dene the virtual link on Device A, enter the following commands.
device A(config)# router ospf
device A(config-ospf-router)# area 2
device A(config-ospf-router)# area 1
device A(config-ospf-router)# area 1 virtual-link 209.157.22.1
device A(config-ospf-router)# write memory
Enter the following commands to
congure the virtual link on Device C.
device C(config)# router ospf
device C(config-ospf-router)# area 0
device C(config-ospf-router)# area 1
device C(config-ospf-router)# area 1 virtual-link 10.0.0.1
Syntax: [no] area { ip-addr | num } [ virtual-link router-id [ authentication-key string | dead-interval num | hello-interval num |
retransmit-interval num | transmit-delay num | md5-authentication key-activation-wait-time num | md5-authentication key-id num
key [ 0 | 1 ] string ] ]
The area ip-addr and num parameters specify the transit area.
The virtual-link router-id parameter
species the router ID of the OSPF router at the remote end of the virtual link. To display the router
ID on a device, enter the show ip command.
Modify virtual link parameters
OSPF has some parameters that you can modify for virtual links. Notice that these are the same parameters as the ones you can modify
for physical interfaces.
You can modify default values for virtual links using the following CLI command at the OSPF router level of the CLI, as shown in the
following syntax:
Syntax: [no] area { ip-addr | num } [virtual-link router-id dead-interval num | hello-interval num | retransmit-interval num | transmit-
delay num | authentication-key string | md5-authentication key key-string | md5-authentication key-activation-wait-time num ]
Virtual link parameter descriptions
You can modify the following virtual link interface parameters:
area ip-addr | num The IP address or number of the transit area.
virtual-link router-id The router ID of the OSPF router at the remote end of the virtual link.
dead-interval num The number of seconds that a neighbor router waits for a hello packet from the current router before declaring the router
down. The value can be from 1 - 65535 seconds. The default is 40 seconds.
hello-interval num The length of time between the transmission of hello packets. The range is 1 - 65535 seconds. The default is 10 seconds.
retransmit-interval num The interval between the re-transmission of link state advertisements to router adjacencies for this interface. The range is 0 -
3600 seconds. The default is 5 seconds.
transmit-delay num The period of time it takes to transmit Link State Update packets on the interface. The range is 0 - 3600 seconds. The
default is 1 second.
authentication-key string This parameter allows you to assign dierent authentication encryption methods on a port-by-port basis. OSPF supports
three methods of authentication for each interface: none, simple encryption, and base 64 encryption. Only one encryption
method can be active on an interface at a time.
Conguring OSPF
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