Subject: [OSPF] Assign router address when only unnumbered I/Fs?

From: Joakim Tjernlund <[email-masked]>
Date: Mon, 10 Aug 2009 20:59:49 +0200

I got routers which only have unnumbered PtoP interfaces and I wonder
how to advertise a host route as described in RFC 2328:
[2]It is possible for all of a router's interfaces to be unnumbered
    point-to-point links.  In this case, an IP address must be assigned
    to the router.  This address will then be advertised in the router's
    router-LSA as a host route.

The first that comes to mind is to just assign an IP address/32 to
the loopback or dummy interface and start OSPF on that I/F. However, you
can only assign one area to that I/F. How have other people
solved this?
Ideally there would be a command that lets me assign a
IP address which will be advertised in all areas.

 Jocke

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From: Dave Katz <[email-masked]>
Date: Mon, 10 Aug 2009 17:08:55 -0600

A router must have at least one IP address in it somewhere, be it  
bound to a loopback or whatnot.

There's nothing wrong with advertising it in multiple areas, though  
particular implementations may or may not let you do so.  Putting it  
in only one area and advertising a summary into other areas would have  
the same effect at forwarding time.

Lots of room for implementation choices here.

--Dave

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From: Joakim Tjernlund <[email-masked]>
Date: Tue, 11 Aug 2009 02:24:05 +0200

Hi Dave :)

> bound to a loopback or whatnot.

Yes.
> the same effect at forwarding time.

But you may not be connected to the backbone in all cases.

> Lots of room for implementation choices here.

Yes, do you know of any? I Would be really like to use some existing template.

 Jocke

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From: Dave Katz <[email-masked]>
Date: Mon, 10 Aug 2009 20:40:41 -0600

> But you may not be connected to the backbone in all cases.

True, though it would be an odd box that was configured to be in  
multiple areas, none of which were the backbone.

> Yes, do you know of any? I Would be really like to use some existing  

There are policy languages on multiple vendors' routers that can do  
all sorts of stuff.  Or one could imagine having a command that says  
"advertise the loopback address in all areas."  Or you could imagine  
advertising the loopback address by default in any area that didn't  
have a numbered interface bound to it.  Etc.

--Dave