| 33.10. OSPF Virtual links table | ||
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 | Chapter 33. OSPF - Open Shortest Path First |  |
| 33.10. OSPF Virtual links table | ||
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| | Chapter 33. OSPF - Open Shortest Path First | |
The table of OSPF Virtual links holds information about Virtual Links.
It is possible to define areas in such a way that the backbone area (0.0.0.0) is no longer contiguous. In this case, the system administrator must restore backbone area connectivity by configuring virtual links.
Virtual links can be configured between any two backbone routers that have an interface to a common non-backbone area. Virtual links belong to the backbone area.
The protocol treats two routers joined by a virtual link as if they were connected by an unnumbered point-to-point network. On the graph of the backbone area, two such routers are joined by arcs whose costs are the intra-area distances between the two routers.
The routing protocol traffic that flows along the virtual link uses intra-area routing only.
Commands for managing the table of OSPF Virtual links are the following:
This command shows all currently defined OSPF Virtual Links:
[19:40:25] ABILIS_CPX:d ospf vl
- Not Saved (SAVE CONF), Not Refreshed (INIT) ---------------------------------
-------------------------------------------------------------------------------
REM-RID: AREA: HELLO: RXMT: TRDEL: DEAD: PWD: KEYID:
MD5KEY:
-------------------------------------------------------------------------------
001.001.001.001 001.001.001.001 10 5 1 60 0
001.001.001.002 001.001.001.001 10 5 1 60 0
-------------------------------------------------------------------------------Meaning of the parameters:
REM-RIDThe Router ID of a remote router that is located in other end of VL.
AREAArea ID of area that is used as transit area for this Virtual Link.
HELLOThe length of time, in seconds, between the Hello Packets that the router sends on the other point of VL. This value is advertised in the router's Hello Packets. It must be the same for both routers attached to a VL. The smaller the Hello Interval, the faster topological changes will be detected, but more OSPF routing protocol traffic will ensue.
RXMTThe number of seconds between link state advertisement retransmissions, for adjacencies belonging to this VL.
TRDELThe estimated number of seconds it takes to transmit a Link State Update Packet over this VL.
DEADAfter ceasing to hear a router's Hello Packets, the number of seconds before its neighbor declare the router down. This is also advertised in the router's Hello Packets in their Router Dead Interval field. This value again must be the same for both routers attached to a VL.
PWDThis parameter allows setting the Authentication password. Strings of up to 8 ASCII characters in the range [33..126] are accepted. Spaces are not allowed. The case of the entered password is preserved. The character string contains a value of a password.
MD5KEYThis parameter allows setting the MD5 secret key. Strings of up to 16 ASCII characters in the range [33..126] are accepted. Spaces are not allowed. The case of the entered key is preserved. A shared secret key is configured in all routers attached to a common network/subnet. For each OSPF protocol packet, the key is used to generate/verify a "message digest" that is appended to the end of the OSPF packet. The message digest is a one-way function of the OSPF protocol packet and the secret key. Since the secret key is never sent over the network in the clear, protection is provided against passive attacks. The algorithm's used to generate and verify the message digest is specified implicitly by the secret key. This specification completely defines the use of OSPF Cryptographic authentication when the MD5 algorithm is used.
KEYIDThis field identifies the algorithm and secret key used to create the message digest appended to the OSPF packet. Key Identifiers (Key ID) must be set equal at the two ends of the VL.
This command adds a new entry to the OSPF Virtual Links table, identified by the specified Remote Router ID and Area ID. The command also sets the eventually indicated optional parameters to the specified values.
[16:40:20] ABILIS_CPX:a ospf vl rem-rid:001.000.000.000 area:002.000.000.000COMMAND EXECUTED [19:40:25] ABILIS_CPX:d ospf vl- Not Saved (SAVE CONF), Not Refreshed (INIT) --------------------------------- ------------------------------------------------------------------------------- REM-RID: AREA: HELLO: RXMT: TRDEL: DEAD: PWD: KEYID: MD5KEY: ------------------------------------------------------------------------------- 001.001.001.001 001.001.001.001 10 5 1 60 0 001.001.001.002 001.001.001.001 10 5 1 60 0 001.000.000.000 002.000.000.000 10 5 1 60 0 -------------------------------------------------------------------------------
This command deletes an entry from the OSPF Virtual Links table, identified by the specified Remote Router ID and Area ID.
[16:40:20] ABILIS_CPX:c ospf vl rem-rid:001.000.000.000 area:002.000.000.000COMMAND EXECUTED [19:40:25] ABILIS_CPX:d ospf vl- Not Saved (SAVE CONF), Not Refreshed (INIT) --------------------------------- ------------------------------------------------------------------------------- REM-RID: AREA: HELLO: RXMT: TRDEL: DEAD: PWD: KEYID: MD5KEY: ------------------------------------------------------------------------------- 001.001.001.001 001.001.001.001 10 5 1 60 0 001.001.001.002 001.001.001.001 10 5 1 60 0 -------------------------------------------------------------------------------
This command sets to new values the parameters of the Virtual Link entry, identified by the specified Remote Router ID and Area ID.
[16:40:20] ABILIS_CPX:s ospf vl rem-rid:001.001.001.001 area:001.001.001.003COMMAND EXECUTED [19:40:25] ABILIS_CPX:d ospf vl- Not Saved (SAVE CONF), Not Refreshed (INIT) --------------------------------- ------------------------------------------------------------------------------- REM-RID: AREA: HELLO: RXMT: TRDEL: DEAD: PWD: KEYID: MD5KEY: ------------------------------------------------------------------------------- 001.001.001.001 001.001.001.003 10 5 1 60 0 001.001.001.002 001.001.001.001 10 5 1 60 0 -------------------------------------------------------------------------------
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| 33.9. OSPF Ranges table |  | 33.11. Deploying OSPF |