Subject: Re: Re: Re: draft-ietf-l3vpn-ospf-2547-01.txt query

From: "Karthikeyan Subramaniam" <[email-masked]>
Date: 5 May 2004 11:27:08 -0000

Hello,

Can anybody in the list help me  in producing a scenario (in VPN) where and why do we need to distinguish real AS-external routes and external routes generated through standard BGP/OSPF interaction mechanism ?

Thanks in advance.
With regards,
S.Karthikeyan

On Tue, 04 May 2004 Karthikeyan Subramaniam wrote :
>   Anand,
>
>
>   Can you produce a scenario (in VPN) where and why do we need to distinguish real AS-external routes and external routes generated through standard BGP/OSPF interaction mechanism ?
>
>with regards,
>S.Karthikeyan
>
>
>On Fri, 30 Apr 2004 Anand Oswal wrote :
> >Karthikeyan,
> >
> >The remote CE routers of the same VPN, need to appear as if they are
> >part of the same OSPF domain, that is why we carry Type 1,2,3 LSAs
> >as Type 3.
> >
> >If you carry all your routes as AS External, how would you know which
> >ones
> >are the "real" Ext routes
> >
> >Thanks
> >Anand
> >
> >Karthikeyan Subramaniam wrote:
> > >
> > > Hello,
> > >
> > >     As stated in the draft draft-ietf-l3vpn-ospf-2547-01.txt,
> > >
> > >    "Per [VPN], the VPN routes are distributed among the PE routers by
> > >    BGP.  If the PE uses OSPF to distribute routes to the CE router, the
> > >    standard procedures governing BGP/OSPF interactions [OSPF] would
> > >    cause routes from one site to be delivered to another as AS-external
> > >
> > >    routes (in type 5 LSAs).  This is undesirable; it would be much
> > >    better to deliver such routes in type 3 LSAs (as inter-area routes),
> > >    so that they can be distinguished from any "real" AS-external routes
> > >    that may be circulating in the VPN. (That is, so that they can be
> > >    distinguished by OSPF from routes which really do not come from
> > >    within the VPN.)"
> > >
> > >    So the query is why do we need to distinguish As-external routes from inter-area routes from VPN perspective??? (I guess Type-3 LSAs are generated for proper database synchronization from OSPF perspective, is there any other reason???)
> > >
> > > Thanks in advance
> > > S.Karthikeyan
>
>
>