Re: EIGRP+PPP

Just to add to whats being said here.

This behaviour was useful from the days when we used Modems to connect to
the Internet (My grandma's days). You needed to know how to connect to the
pop router and it needed to know how to connect to you. So you had to run
PPP.

Nowadays, we use this behavior to provide reachability, since PPP adds
neighbor's IP address as a host route in your routing table the end points
no longer need to be in the same subnet to have NLRI to each other.

Why remove it?
Going back to Rocky Marciano days, when we had ISDN and we needed to use the
ISDN link as a backup to a frame or other types of links. The second you did
an "Encap ppp" under your BRI interface, ppp added the /32 host routes
automatically (Default behaviour), now....let's say you are running OSPF
over the main and your ISDN interfaces, we both know that OSPF's hellos will
keep the ISDN link UP, unless you do an "IP OSPF DEMAND-CIR" under your BRI
interface, which maintained the OSPF neighbor adjacency while bringing the
ISDN link down, the ONLY time the ISDN link would ever come up is when OSPF
detected a topology change. If you did not do this, end of the month you
would get a bill for few thousand dollars for your ISDN usage. An RGE event
(Resume Generated Event).

But once OSPF establishes a nieghbor adjacency through the ISDN link and
brings the ISDN link down, from PPP's perspective, the link was down so it
removed the /32 route. Once the route was removed, from OSPF's perspective
we had a topology change, so OSPF will bring the link back up to convey the
changes, and the cycle repeated itself, so the end result was that the ISDN
link kept on flapping. So what we had to do was to remove the host route by
configuring "No peer neighbor-route".

I hope this helped.

On Wed, Sep 1, 2010 at 2:02 PM, Marcelo Rosa <MRosa_at_multirede.com.br> wrote:

> These /32 routes exist to address the issue when you use ip unumbered and
> the borrowed ip addresses are not in the same subnet. As Karim stated, they
> make reachability possible. I you don4t need it, you can use the no peer
> neighbor-route to eliminate it.
>
> HTH,
>
>
> Marcelo Rosa
> http://codornafatiada.wordpress.com
> http://projectccie.wordpress.com
> Sent from my Ollivetti Lettera 82
>
> "It4s supposed to be hard. If it wasn4t hard everyone would do it. The hard
> is what makes it great."
>
>
>
> -----Mensagem original-----
> De: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] Em nome de karim
> jamali
> Enviada em: quarta-feira, 1 de setembro de 2010 17:57
> Para: masroor ali; Cisco certification
> Assunto: Re: EIGRP+PPP
>
> Dear Masroor,
>
> This has nothing to do with EIGRP. Just run PPP on both sides of the
> interface and you will see that peer neighbor route will always install the
> host route for the other side. This is PPP's normal behavior, well I kind
> of
> think about it "it is just 2 people on the link" so they must be able to
> reach each other. You can also try it with different subnets (1.1.1.1 and
> 3.3.3.3) for instance and you will see that the peer neighbor route makes
> reachability possible.
>
> HTH,
>
> Best Regards,
>
> On Wed, Sep 1, 2010 at 11:46 PM, masroor ali <masror.ali_at_gmail.com> wrote:
>
> > can you please describe more???
> >
> > On Thu, Sep 2, 2010 at 1:44 AM, rajeevan singh <rajeevansingh_at_gmail.com
> > >wrote:
> >
> > > so no peer neighbor-route , on the link ( interface.)
> > >
> > > On Thu, Sep 2, 2010 at 2:12 AM, masroor ali <masror.ali_at_gmail.com>
> > wrote:
> > >
> > >> hi,
> > >>
> > >> when using ppp with eigrp, why it shows /32 neighbor route in local
> > >> routing
> > >> table??? and using no peer neighbor-route it doesnt show /32 route
> > >> what's the idea?
> > >>
> > >> --
> > >> Regards,
> > >> Masroor Ali
> > >>
> > >>
> > >> Blogs and organic groups at http://www.ccie.net
> > >>
> > >>
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> > >>
> > >>
> > >
> >
> >
> > --
> > Regards,
> > Masroor Ali
> >
> >
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>
>
> --
> KJ
>
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