Re: Just shy of OT MPLS Question

Well to do this you would have to solve the next hop problem possibly
forming neighbors based on interface for each hop and then set next hop
self. You would also have to either turn off the IGP or change AD for
BGP. I think that pretty much throws TE out the window. Ridiculous but
not impossible.

From:
Bryan Bartik <bbartik_at_ipexpert.com>
To:
ALL From_NJ <all.from.nj_at_gmail.com>
Cc:
Keegan.Holley_at_sungard.com, Cisco certification <ccielab_at_groupstudy.com>
Date:
12/21/2009 10:49 PM
Subject:
Re: Just shy of OT MPLS Question
Sent by:
<nobody_at_groupstudy.com>

Keegan,

The main problems I find is that you get inconsistencies between
labels/next-hops. Consider this topology with no OSPF and IBGP+Send-label
instead:

PE1----P("RR")----PE2

In IBGP, next-hops do not change and the label gets reflected along with
the
route. This means PE1 sees the loopback to PE2 with an imp-null label that
PE2 generated for itself. When PE1 sends packets toward PE2, there is no
"outer label" and the VPN label is exposed to the P router and breaks the
LSP.

There are several tweaks you can try but I never got it to work, although
I
left some theories on the table :-)

On Mon, Dec 21, 2009 at 8:19 PM, ALL From_NJ <all.from.nj_at_gmail.com>
wrote:

> lol ... you got me. Yes, the LDP protocol exchanges labels based on ...
?
>
> I was not technical enough in my quick answer. ;-)
>
> I am not sure why Cisco chose this ... (other than lower overhead on
core /
> P routers)
>
> I am not very knowledgeable with Juniper, but I understand that Juni can
do
> this with BGP? Probably someone smarter than me knows more about Juni
...
> I
> just have not ever studied them.
>
> What saith thee Juni guys? Super Scott has some Juni certs, maybe we
can
> get the super Scott to respond.
>
> I am studying for a cvoice test! lol ... I think I am trying to fit too
> much into my little brain.
>
> Have a great night,
>
> Andrew
>
>
> On Mon, Dec 21, 2009 at 10:01 PM, <Keegan.Holley_at_sungard.com> wrote:
>
> >
> > Thanks for responding. Technically the outer labels come from LDP or
> RSVP.
> > They are then mapped to the route for the endpoints of the
LSP/tunnel.
> I
> > was just wondering why this couldn't be built with BGP instead of an
IGP.
> >
> > ALL From_NJ <all.from.nj_at_gmail.com> wrote on 12/21/2009 09:43:40 PM:
> >
> >
> > > Good evening Sir,
> > >
> > > I am pressed for time, so please forgive the quick and short
> > > response. Outer labels come from IGP, and not from BGP ... so no
> > > way to use BGP for this. HTH,
> > >
> > > Andrew Lee Lissitz
> > >
> >
> > > On Mon, Dec 21, 2009 at 9:07 PM, <Keegan.Holley_at_sungard.com> wrote:
> > > Does anyone know why you cannot use BGP routes to build MPLS
tunnels.
> Is
> > > it the obvious (slow hello timers, possibly next hop ambiguity) or
is
> > > there something inherent in the protocol suite (MPLS, RSVP, LDP)
that
> > > makes it impossible.
> > > Not that I would ever want to... Just a little curious.
> > >
> > >
> > > Blogs and organic groups at http://www.ccie.net
> > >
> > >
Received on Tue Dec 22 2009 - 21:40:28 ART