Re: draft-eng-nalawade-ospf-tunnel-cap-00.txt

[Gargi Nalawade <[e-mail]>]

Rahul,

Rahul Aggarwal wrote:
>
> Hi Gargi,
>
> > its domain using an IGP and redistribute only the inter-AS information on
> > the border PEs.
>
> This is another flaw with doing this in IGP. A BGP only solution doesn't

A BGP-only solution *requires* BGP. That is the only flaw with just doing
this via BGP.

> require redistribution between IGP and BGP.
>
> >
> > Not necessarily. Depends on the application. You are narrowing down the scope
> > to a particular application - which is why you think PE. I agree that common
> > scenarios would be PE-to-PE. But that does not mean that there won't be scenarios
> > that have P routers as endpoints. TE-tunnels is one example.
> >
>
> Please explain how/why tunnel capabilities will be used by TE tunnels.

There are numerous examples out there. Look at draft-vasseur-mpls-ospf-te-cap-00.txt

>
> > Also note that this draft is a framework for tunnel endpoint signalling and
> > how and where it is deployed/used and whether the tunnel endpoints are PEs
> > or Ps depends on the specific application a Provider or an Enterprise has
> > in mind.
> >
>
> Can you articulate the applications where this information is needed on
> the P routers ?

I just named one. This is not limited/targeted at P routers though. There
could be enterprise routers that do not run BGP that need tunneling mechanisms.
Sandy's email mentioned an example for that as well.

> > > > learnt through an IGP to resolve the nexthop to BGP prefixes. But in
> > > > the presence of tunnels, this reachability is not sufficient
> > > and the
> > > > reachability via the tunnels has to be propagated as well.
> > >
> > > For route resolution, the BGP next-hop needs to be reachable. The BGP
> > > next-hop will be the tunnel endpoint address. This in turn will be an IGP
> > > route. Why is this not sufficient ?
> >
> > Because the reachability would be through the tunnel. Unless the tunnel
>
> The control traffic reachability is through the hop by hop path to the
> tunnel endpoint. Data traffic takes the tunnel.

Data traffic cannot take the tunnel path until -

1) the control-plane IGP route-reachability has converged
2) the Tunnel reachability has converged

Today - IGPs can give us 1). What is missing is 2) - which is what this draft
proposes to add.

Thanks,
Gargi