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Re: [OSPF] multilple numbered PtoP links with the same local IP address

On Aug 14, 2009, at 11:03 AM, Joakim Tjernlund wrote:


Acee Lindem <acee at lindem.com> wrote on 14/08/2009 16:23:15:


On Aug 14, 2009, at 3:14 AM, Joakim Tjernlund wrote:


Acee Lindem <acee at lindem.com> wrote on 14/08/2009 00:13:48:
Is there something in the OSPF spec which prevents it from operate 
on multiple numbered PtoP interfaces with the same local IP
address?

I have that working, but there are arguments that this is
allowed by
OSPF, i.e, ethier use unnumbered links or unique local IP
addresses.

 Jocke


Got some comments on this but nothing conclusive, I really want
to know. Acee, what do you think?
Since there is only a type 1 (router link) in the Router-LSA for each 
unnumbered link, it makes no difference how many use the same IP
address.


Right, but how about multiple NUMBERED PtoP interfaces with the
same local IP address?


I'd argue that if your configuration supports this, all but one of
the interfaces is unnumbered.


hmm, please clarify. I do mean treating each and every PtP
as a numbered PtP link. Is there something that prohibits
this in the spec? Of course not all routers will
be able to handle this but in that case it would be a
limitation in the impl.

Is it allowed to have numbered on one side of the link
and unnumbered on the other side?


Yes - this is fine.

Thanks,
Acee










Then there will be multiple identical
type 3 too.


Even though it is non-standard, I don't see any problems. I believe
Dave alluded to the fact that some OSPF implementations may have ABR
SPF optimizations which can have problems when the same address is
advertised in multiple addresses - I know fixed some problems here in
one implementation.


Yeah, when one only uses the router LSAs to identify the interface
you are in trouble.



Acee



 Jocke