VIRTUAL_LINK statement

Use the VIRTUAL_LINK statement to configure a virtual link between two area border routers. To maintain backbone connectivity you must have all of your backbone routers interconnected either by permanent or virtual links. Virtual links are considered to be separate router interfaces connecting to the backbone area. Therefore, you are asked to specify many of the interface parameters when configuring a virtual link.

Virtual links can be configured between any two backbone routers that have an interface to a common nonbackbone, nonstub area. Virtual links are used to maintain backbone connectivity and must be configured at both endpoints.

Tip: OSPF virtual links are not to be confused with Virtual IP Address support (VIPA).

Parameters

Virtual_Endpoint_RouterID

Router ID of the virtual neighbor (other endpoint). Router IDs are entered in the same form as IP addresses.

Links_Transit_Area

This is the nonbackbone, nonstub area through which the virtual link is configured. Virtual links can be configured between any two area border routers that have an interface to a common nonbackbone and nonstub area. Virtual links must be configured in each of the link's two endpoints. Valid values are any area defined by the AREA statement, except 0.0.0.0.

Retransmission_Interval

Sets the frequency (in seconds) of retransmitting link-state update packets, link-state request packets, and database description packets. Valid values are from 1 - 65 535 seconds.

Guideline: If this parameter is set too low, needless retransmissions occur that could affect performance and interfere with neighbor adjacency establishment. It should be set to a higher value for a slower machine.

Transmission_Delay

This parameter is an estimate of the number of seconds that it takes to transmit link-state information over the virtual link. Each link-state advertisement has a finite lifetime of 1 hour. As each link-state advertisement is sent out from this virtual link, it is aged by this configured transmission delay. Valid values are in the range 1 - 65 535 seconds.

Hello_Interval

This parameter defines the number of seconds between OSPF Hello packets being sent out from this virtual link. Valid values are in the range 1 - 255 seconds. The Hello_Interval should be set higher than the same value used on the intervening, actual OSPF interfaces.

DB_Exchange_Interval

The interval in seconds that the database exchange process cannot exceed. If the interval elapses, the procedure is restarted. This value must be larger than the Hello_Interval. If no value is specified, the DB_Exchange_Interval is set to the Dead_Router_Interval. Valid values are 2 - 65 535.

Dead_Router_Interval

The interval in seconds, after not having received an OSPF Hello, that the neighbor is declared to be down. This value must be larger than the Hello_Interval. Valid values are 2 - 65 535. The dead router interval should be set higher than the same value used on the intervening, actual, OSPF interfaces.

Authentication_Key

The value of the authentication key for this interface. This value must be the same for all routers attached to a common medium. The coding of this parameter depends on the authentication type being used on this interface.

For authentication type none, this parameter is not required and is ignored if coded.

For authentication type password, code the password for OSPF routers that are attached to this subnet. Valid values are any characters from EBCDIC code page 1047 up to 8 characters in length coded within double quotation marks or any hexadecimal string up to 8 bytes (16 hex characters) long that begins with 0x.

For authentication type MD5, code the 16-byte MD5 authentication key for OSPF routers attached to this subnet. This value can be coded in one of the following ways:

• The standard method is with a 16-byte hexadecimal string beginning with 0x (0x plus 32 hexadecimal characters). In some cases, pwtokey can be used to generate hexadecimal MD5 keys. See z/OS Communications Server: IP System Administrator's Commands for more information.
• An additional method, which provides compatibility with Cisco, Extreme, and other vendor routers that use a Cisco-compatible CLI interface is to code the MD5 key as an ASCII string, specified in double quotation marks prefixed with A. For example, to be compatible with this Cisco key definition, use the following code:

  ip ospf message-digest-key 4 md5 ABCDEFGHIJKLMNOP

  This value would be coded in OMPROUTE as follows:

  AUTHENTICATION_KEY_ID =4
  AUTHENTICATION_KEY = A"ABCDEFGHIJKLMNOP"

Authentication_Key_ID

The identifier of the authentication key defined with the AUTHENTICATION_KEY keyword. This is a constant numeric value from 0 - 255, with a default value of 0. It is only relevant when MD5 cryptographic authentication is employed on the virtual link; otherwise, it is ignored. This field is provided for compatibility with other routers which might require identification of a key identifier with the authentication key.

Authentication_Type

The security scheme to be used over the virtual link. If not specified, the statement takes on the default value specified for the backbone area. Valid values for authentication types are MD5, which indicates MD5 cryptographic authentication as described in Appendix D of RFC 2328; PASSWORD, which indicates a simple password; or NONE, which indicates that no authentication is necessary to pass packets. Both hosts attached to the virtual link must be configured with the same security scheme.