Router ID and Virtual-link

Unanswered Question
Dec 10th, 2007
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Hi All,

1)under router ospf 1 process

router-id (Is it mandatory that this IP address should exist for any of the interface in the router ?

2) When establishing the virtual link between 2 ABR routers , is it mandatory that Router-ID should be reachable between the routers

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Overall Rating: 5 (2 ratings)
Danilo Dy Mon, 12/10/2007 - 04:43
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The router ID is the component of every OSPF exchange, including HELLO packets and link-state advertisements (LSAs). It is desirable to have a router ID that does not change. Therefore, configure loopback IP address and use it in "router-id" command after "router ospf process_number".

The answer for both question is yes. In the second question, to configure virtual-link, the command is "area area_id virtual-link router_id ", therefore the router ID should be reachable with each other to exchange messages.



mohammedmahmoud Mon, 12/10/2007 - 05:03
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As Dandy pointed out, configuring a RID is not mandatory but recommended especially when having virtual-links, but for the second question, no, the RID need not be reachable its just an ID even when having virtual-links, the RID still doesn't need to be reachable, its just an ID for the router.


Mohammed Mahmoud.

Danilo Dy Mon, 12/10/2007 - 05:07
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Hi Mohammed,

Thanks for pointing that out :)

Welcome back and congrats to your number!



vidyaprakash Mon, 12/10/2007 - 05:15
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Hi ,

Pls correct me my understanding with your comments.

1) I need to use Router ID under OSPF process.(Router-ID IP should be in use for any Physical or logical IP address in the router)

2) When i use Router-ID IP address , it is not require to advertise RID IP network statement in the ospf process .



Richard Burts Mon, 12/10/2007 - 05:26
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As to your first statement: you may specify routerID under the OSPF process and it is generally considered best practice to specify the routerID. But it is not required. If you do specify the routerID then it is best practice to use the IP address of an interface on the router as the routerID, but that is not required.

As to your second statement: yes when you specify the routerID it is not necessary to advertise that address by a network statement in the OSPF process.



mohammedmahmoud Mon, 12/10/2007 - 05:31
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Hi Dandy,

Thank you very much, i am really glade to be back, and of course with my number :)


1) It is recommended to configure your RID manually under your process, the RID is in the IPv4 format, but it is not required to be an IP address configured under any physical or logical interface on this router (as a best practice we always use a loopback interface IP).

2) The RID is not required to be reachable in the routing context, its just an ID.


Mohammed Mahmoud.


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