To define an OSPF virtual link, use thearea virtual-link router configuration command with the optional parameters. To remove a virtual link, use the no form of this command.
area area-id virtual-link router-id [hello-interval seconds] [retransmit-interval seconds]
[transmit-delay seconds] [dead-interval seconds] [ [authentication-key key]
[message-digest-key keyidmd5 key]]
no area area-id virtual-link router-id [hello-interval seconds] [retransmit-interval seconds]
[transmit-delay seconds] [dead-interval seconds] [ [authentication-key key]
[message-digest-key keyidmd5 key]]
no area area-id
area-id Area ID assigned to the transit area for the virtual link. This can be either a decimal value or a valid IP address. There is no default.
router-id Router ID associated with the virtual link neighbor. The router ID appears in the show ip ospf display. It is internally derived by each router from the router's interface IP addresses. This value must be entered in the format of an IP address. There is no default.
hello-interval seconds (Optional) Time in seconds between the hello packets that the Cisco IOS software sends on an interface. Unsigned integer value to be advertised in the software's hello packets. The value must be the same for all routers and access servers attached to a common network. The default is 10 seconds.
retransmit-interval seconds (Optional) Time in seconds between link state advertisement retransmissions for adjacencies belonging to the interface. Expected round-trip delay between any two routers on the attached network. The value must be greater than the expected round-trip delay. The default is 5 seconds.
transmit-delay seconds (Optional) Estimated time in seconds it takes to transmit a link state update packet on the interface. Integer value that must be greater than zero. Link state advertisements in the update packet have their age incremented by this amount before transmission. The default value is 1 second.
dead-interval seconds (Optional) Time in seconds that a software's hello packets are not seen before its neighbors declare the router down. Unsigned integer value. The default is four times the hello interval, or 40 seconds. As with the hello interval, this value must be the same for all routers and access servers attached to a common network.
authentication-key key (Optional) Password to be used by neighboring routers. Any continuous string of characters that you can enter from the keyboard up to 8 bytes long. This string acts as a key that will allow the authentication procedure to generate or verify the authentication field in the OSPF header. This key is inserted directly into the OSPF header when originating routing protocol packets. A separate password can be assigned to each network on a per-interface basis. All neighboring routers on the same network must have the same password to be able to route OSPF traffic. The password is encrypted in the configuration file if the service password-encryptioncommand is enabled. There is no default value.
message-digest-key keyid md5 key (Optional) Key identifier and password to be used by neighboring routers and this router for MD5 authentication. The keyid is a number in the range 1 to 255. The key is an alphanumeric string of up to 16 characters. All neighboring routers on the same network must have the same key identifier and key to be able to route OSPF traffic. There is no default value.
area-id: No area ID is predefined.
router-id: No router ID is predefined.
hello-interval seconds: 10 seconds
retransmit-interval seconds: 5 seconds
transmit-delay seconds: 1 second
dead-interval seconds: 40 seconds
authentication-key key: No key is predefined.
message-digest-key keyidmd5 key: No key is predefined.
Router configuration
| Release | Modification | 10.0 | This command was introduced. |
11.0 | The following keywords and arguments were added:
|
|---|
In OSPF, all areas must be connected to a backbone area. If the connection to the backbone is lost, it can be repaired by establishing a virtual link.
The smaller the hello interval, the faster topological changes will be detected, but more routing traffic will ensue.
The setting of the retransmit interval should be conservative, or needless retransmissions will result. The value should be larger for serial lines and virtual links.
The transmit delay value should take into account the transmission and propagation delays for the interface.
The Cisco IOS software will use the specified authentication key only when authentication is enabled for the backbone with the areaarea-idauthentication router configuration command.
The two authentication schemes, simple text and MD5 authentication, are mutually exclusive. You can specify one or the other or neither. Any keywords and arguments you specify after authentication-key keyor message-digest-key keyidmd5 key are ignored. Therefore, specify any optional arguments before such a keyword-argument combination.
Each virtual link neighbor must include the transit area ID and the corresponding virtual link neighbor's router ID in order for a virtual link to be properly configured. Use the show ip ospfEXEC command to see the router ID.
To remove the specified area from the software configuration, use the command no area area-id (with no other keywords). That is, no areaarea-id removes all area options, such as area authentication, area default-cost, area nssa, area range, area stub, and area virtual-link .
The following example establishes a virtual link with default values for all optional parameters:
router ospf 201 network 36.0.0.0 0.255.255.255 area 36.0.0.0 area 36.0.0.0 virtual-link 36.3.4.5
The following example establishes a virtual link with MD5 authentication:
router ospf 201 network 36.0.0.0 0.255.255.255 area 36.0.0.0 area 36.0.0.0 virtual-link 36.3.4.5 message-digest-key 3 md5 sa5721bk47
| Command | Description |
|---|---|
| area authentication | Enables authentication for an OSPF area. |
| service password-encryption | Encrypts passwords. |
| show ip ospf | Displays general information about OSPF routing processes. |
Printed for apswan@ctr.ap.nic.in on Wed Mar 5 22:32:57 PST 2003
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