Subject: RE: MPLS/BGP routing question

From: Javier Antich <[email-masked]>
Date: Thu, 28 Sep 2000 18:28:22 +0200

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.

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_________________________________________________________________________
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Dpto Pre-Venta.	                                       Torre Metropolitana

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	-----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: Javier Antich <[email-masked]>
Date: Fri, 29 Sep 2000 09:18:59 +0200

One of the main advantages of using MPLS in the core is to avoid running BGP
in the core routers, as long as they only switch packets (except from those
for IGP routing advertisments) but not route them. Of course, if the MPLS
cloud fails due to, for example, a software bug, the core routers would need
to route packets according to their routing tables. You could have the core
routers running BGP and MPLS, but most of the time BGP routes would not be
used at all. If the MPLS code fails, I am not sure whether your services
(like VPNs, Traffic Engineered Paths, ...) would go on working, even if you
have BGP running in your core routers.

                                                              Plaza Ciudad
de Viena, 6 -2º 
                                                              28040 MADRID.
(ESPAÑA).

	-----Mensaje original-----
	De:	Chris Flores [SMTP:[email-masked]]
	Enviado el:	jueves 28 de septiembre de 2000 20:18
	Para:	'Javier Antich'; Michel Redondo Ferrero
	CC:	[email-masked]
	Asunto:	RE: MPLS/BGP routing question

	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.

_________________________________________________________________________
	Javier Antich Romaguera.                          KERN DATANET
-TELINDUS
	ESPAÑA
	Dpto Pre-Venta.	                                       Torre
Metropolitana

	                                                              Plaza
Ciudad
	de Viena, 6 -2º 
	                                                              28040
MADRID.
	(ESPAÑA).

		-----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,

		The question:

		Michel Redondo Ferrero

---

From: Danny McPherson <[email-masked]>
Date: Fri, 29 Sep 2000 11:01:16 -0600

> I don't  agree.  I think that  even with respect to  public Internet routes,
> there are a  number of advantages to NOT distributing all  the routes to all
> the core  routers.  I think it  is a perfectly  valid use of MPLS  to tunnel
> packets through the core so as to avoid the need for a full IBGP mesh. 

Of course, pretty much no one has 'true' full IBGP mesh today (i.e. either RRs 
or confederations are used) and pretty much no one has MPLS-only core (today). 
 Given, there are significant advantages with disabling BGP in the core (some 
mentioned in the level3bcp draft, I believe), especially when considering 
stability.

Then again, the complexity of your pseudo full-mesh IBGP network increases 
considerably when you remove a layer of the IP hierarchy (i.e. the IP core) 
and it's now non-congruent to the underlying network topology (e.g. the BGP 
rr-considered-harmful(?) draft a while back, the new wording surrounding 
topologies in RFC 2796, etc..).

-danny

---

From: Chris Flores <[email-masked]>
Date: Fri, 29 Sep 2000 10:56:34 -0500

in-line response...

-----Original Message-----
From: Curtis Villamizar [mailto:[email-masked]]
Sent: Friday, September 29, 2000 10:34 AM
To: Chris Flores
Cc: 'Javier Antich'; Michel Redondo Ferrero; [email-masked]
Subject: Re: MPLS/BGP routing question 

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?

CF: I didn't realize the term optical switch was mentioned. When I refer to
core router, I mean core router - not optical switch. 

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

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

CF: Again, core router - not optical switch.