Subject: RE: MPLS/BGP routing question

From: Chris Flores <[email-masked]>
Date: Thu, 28 Sep 2000 13:18:27 -0500

Interesting, then I have the following question. Let's say the transit
backbone consists of a 3 level hierarchy - core, distribution and access.
BGP is configured such that the access (or edge) routers are route reflector
clients of the distribution routers. Furthermore, the distribution routers
are route reflector clients of the core routers. As Michel Redondo Ferrero
has stated, MPLS VPNs originate and terminate on the access or edge of the
network (in his scenario). Why would you turn off BGP on the core routers?
What if MPLS breaks or fails for any reason (i.e. software bug). Then, how
would routing occur?

Regards.

chris

-----Original Message-----
From: Javier Antich [mailto:[email-masked]]
Sent: Thursday, September 28, 2000 11:28 AM
To: Michel Redondo Ferrero
Cc: [email-masked]
Subject: RE: MPLS/BGP routing question

Core Routers do not need to run BGP because they, in practice don't take
routing decisions with user traffic (I mean traffic comming or going to
Internet), they just switch frames based on their MPLS label. BGP decissions
are made at the edge and packets sent to the BGP next hop through the
corresponding MPLS LSP.

Visite nuestro web: http://www.kerndatanet.com/
<http://www.kerndatanet.com/> 
                               http://www.telindus.es
_________________________________________________________________________
Javier Antich Romaguera.                          KERN DATANET -TELINDUS
ESPAÑA
Dpto Pre-Venta.	                                       Torre Metropolitana

                                                              Plaza Ciudad
de Viena, 6 -2º 
                                                              28040 MADRID.
(ESPAÑA).
e-mail: [email-masked] <mailto:[email-masked]>
TF:  (+34) 91 4560008

	-----Mensaje original-----
	De:	Michel Redondo Ferrero [SMTP:[email-masked]]
	Enviado el:	jueves 28 de septiembre de 2000 8:26
	Para:	[email-masked]
	Asunto:	MPLS/BGP routing question

	Hi,

	Considering the next scenario:

	-Core and Border routers running IS-IS, MPLS
	-VPNs configured in Border routers using BGP/MPLS
	-Border routers running BGP with full-routing

	The question:
	Do Core routers need to run BGP? Is IS-IS enough?

	Thanks in advance for your answers.

	Michel Redondo Ferrero

---

From: Eric Osborne <[email-masked]>
Date: Thu, 28 Sep 2000 14:32:24 -0400

If MPLS breaks, and routing isn't available, then routing wouldn't
occur. :)

Having IP available as a backup path to MPLS is a nice
belt-and-suspenders idea, but there are some services (MPLS VPNs,
circuit transport, etc) that have no way to fall back to a non-MPLS
path.  

eric

---

From: "Brijesh Kumar" <[email-masked]>
Date: Thu, 28 Sep 2000 14:57:26 -0400

The claim that only edge routers need to run BGP/MPLS VPN software
is not true, as you have correctly pointed out. It's not appropriate
to consider the required Route Reflection as an edge router function.

Cheers,
--brijesh
Ennovate Networks Inc.

> From: [email-masked] [mailto:[email-masked]]On Behalf Of Chris
> Flores

---

From: Martin Picard <[email-masked]>
Date: Thu, 28 Sep 2000 15:09:23 -0400

> to consider the required Route Reflection as an edge router function.

You're right, MPLS VPN is not needed only the edge routers but also
on the RRs. But it surely is not a requirement for the backbone routers.

martin

---

From: Eric Rosen <[email-masked]>
Date: Thu, 28 Sep 2000 16:18:23 -0400

Brijesh> The claim that only edge  routers need to run BGP/MPLS VPN software
Brijesh> is  not  true,  as  you   have  correctly  pointed  out.  It's  not
Brijesh> appropriate to  consider the required  Route Reflection as  an edge
Brijesh> router function.

You can sure tell it's the season for political debates ;-)

You're aware,  aren't you,  that route  reflectors don't need  to be  in the
path, and  in fact don't need  to pass data  traffic at all.  I  suppose the
more accurate  statement would be that  the only routers which  need to both
pass traffic and run BGP are the edge routers.

---

From: "Brijesh Kumar" <[email-masked]>
Date: Thu, 28 Sep 2000 16:55:11 -0400

Eric,

I don't think I said that Route Reflectors need to be in the path, or
this function cannot be implemented on an Edge router itself. But
given the performance difference in access routers and core routers,
and the role of a route reflector in applying policies on behalf of
clients, it is pretty obvious that a core router is more suitable for
route reflection function. And we both agree that a router designated
as Route Reflector need to run BGP.

Cheers,

--brijesh

> From: [email-masked] [mailto:[email-masked]]On Behalf Of Eric
> Rosen
> Sent: Thursday, September 28, 2000 4:18 PM
> To: [email-masked]
> Cc: 'Chris Flores'; 'Javier Antich'; 'Michel Redondo Ferrero';
> [email-masked]
> Subject: Re: MPLS/BGP routing question
>
>

---

From: "Satoru Matsushima" <[email-masked]>
Date: Fri, 29 Sep 2000 11:08:29 +0900

> If MPLS breaks, and routing isn't available, then routing wouldn't

When a LSP of PE to PE broken, BGP has no way of LSP broken.
Then, BGP keep up of VPN routes and VPN traffic going to black hole,
until LSP avairable.

As a result, VPN customer can not back up their traffic to any link.

I think this is one of most seriously problem of BGP/MPLS VPN.

--
Satoru Matsushima

---

From: Senthilkumar Rajasekharan <[email-masked]>
Date: Thu, 28 Sep 2000 23:58:26 -0400 (EDT)

> > If MPLS breaks, and routing isn't available, then routing wouldn't

Isn't this the reason why path protection mechanisms were introduced in 
MPLS ? Shouldn't VPN provisioning also include "fault management" ??
Or is this something that is left to the underlying LSRs.

Perhaps someone on this list can enlighten me ?

Thanks,
-Senthil

---

From: Eric Rosen <[email-masked]>
Date: Fri, 29 Sep 2000 11:23:39 -0400

Brijesh> given the performance difference in access routers and core routers,
Brijesh> and the role of a route reflector in applying policies on behalf of
Brijesh> clients, it is pretty obvious that a core router is more suitable for
Brijesh> route reflection function. 

I  think this  is a  bit like  comparing apples  and oranges.   The powerful
packet forwarding  engines that one finds  in core routers don't  do the BGP
protocol  processing work.   The  performance difference  in  edge vs.  core
routers is  pretty irrelevant  in this  context.  In any  event, a  big edge
router with lots  of "high touch" features is going to  be a pretty powerful
beast itself. 

But more  to the  point --  when people  ask "do I  need to  run BGP  in the
core?", they aren't asking what kind  of box makes the best route reflector,
they are  asking whether their  core routers (i.e.,  the ones that  are kept
quite busy moving packets between edges) need to run BGP.

---

From: Eric Rosen <[email-masked]>
Date: Fri, 29 Sep 2000 11:32:14 -0400

Matsushima> When a  LSP of PE to  PE broken, BGP  has no way of  LSP broken.
Matsushima> Then, BGP keep  up of VPN routes and VPN  traffic going to black
Matsushima> hole, until LSP available.

Matsushima> As a result,  VPN customer can not back up  their traffic to any
Matsushima> link.

Matsushima> I think this is one of most seriously problem of BGP/MPLS VPN.

The  situation you  are worried  about is  where there  is  IGP connectivity
between the edges,  but for some reason labeled packets  cannot make it from
one edge to another.  I guess we don't really see this as a realistic failure
scenario.  Sure, buggy software could cause this, but there's a million ways
in which buggy software could cause undetected packet loss.

---

From: Curtis Villamizar <[email-masked]>
Date: Fri, 29 Sep 2000 11:34:01 -0400

In message <[email-masked]>, Chris F
lores writes:
> Why would you turn off BGP on the core routers?

On an optical switch why would you turn it on?

> What if MPLS breaks or fails for any reason (i.e. software bug). Then, how

It wouldn't.  If your optical switches fail, then you can't IP forward
through the control path.

If you can get similar reliability out of the PSC LSPs so that after
failure restoral occurs, even if restoral results in degraded
performance, then you have the same situation in which if the LSP can
be restore, then traffic flow, if it can't be restored, no traffic
flows.  HINT:  Overbooking is a good thing.  CAC is a bad idea.

What happens now if you have a bug in your IGP code or BGP code and
you end up with a persistent routing loop - You can't get there from
here.  If your MPLS code doesn't work or is badly configured (CAC
results in an LSP not coming up at all) expect sililar results.

Curtis

---

From: Curtis Villamizar <[email-masked]>
Date: Fri, 29 Sep 2000 16:26:48 -0400

In message <[email-masked]>, "Brijesh 
> as Route Reflector need to run BGP.

A route reflector need not be a router but it does have to run BGP.
Though common practice is to use the core routers since currently they
must IBGP anyway and generally have the memory and CPU power and a
stable BGP implementation to do it well.

Curtis

---

From: "S.Matsushima" <[email-masked]>
Date: Sat, 30 Sep 2000 10:23:38 +0900

on 00.9.30 0:32 AM, Eric Rosen at [email-masked] wrote:

> one edge to another.

Yes, exactly.

> I guess we don't really see this as a realistic failure

I think that LSP failure was caused by not only buggy software but also
oparation failure.
For example, i) erase a interface as LDP ID ;-< , ii) routes summarization
failure on ospf area,...

IMO, BGP which on PE should has some way to know of LSP failure.
This is for customer.

--
Satoru Matsushima