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

[Acee Lindem <acee at lindem.com>]

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.


> 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.

Acee

>  Jocke