Subject: RE: MPLS routing accross AS boundaries

From: "Peter Ashwood-Smith" <[email-masked]>
Date: Wed, 29 Mar 2000 08:36:29 -0500

Currently the MPLS working group has not addressed this subject in any depth
although there was a draft presented in the routing area group today in
Adelaide that started to talk about solutions.

As far as I know there are basically two ways to attack this problem, or at
least two general flavors. 

piecewise source routing. In this approach you compute a gateway based on
the destination address and then do normal flat source routing to that
gateway. Go through the gateway and repeat. In other words you are doing
piecewise traffic engineering but letting the exterior gateway protocols
figure out which gateway you should be going to next. Obviously there are
problems with this approach since it puts everything though the same
gateway. I actually helped built a piecewise solution like this a while ago.
It has some good advantages in that local (at least local to an AS) repair
is natural to do as are local modification etc. 

hierarchical source routing. This is what ATM does, you compute a hop list
hierarchically against a hierarchical topology database etc. etc. I'm not
sure this approach is appropriate for the Internet due to the massive size
of the problem but I'm really not an ATM hierarchical routing guy.

I would hope that the MPLS working group or the Traffic Engineering working
group can start looking at these issues, possibly with some simulations of
the different approaches against a set of real AS topologies. Some of the
PNNI architects and BGP architects are active members  of the MPLS working
group so you can be sure that it will cause some heated debate ... should be
extremely interesting and challenging.

Cheers,

Peter

	-----Original Message-----
	From:	Andrzej Czerczak [SMTP:Andrzej_Czerczak/[email-masked]]
	Sent:	Tuesday, March 28, 2000 6:04 AM
	To:	[email-masked]
	Subject:	MPLS routing accross AS boundaries

	Hi,
	 Where can I get information on the subject of MPLS QoS routing
accross
	Autonomous System boundaries?

	Thanks
	Andrzej

---

From: "Phani Koganti" <[email-masked]>
Date: Wed, 29 Mar 2000 16:56:08 -0500

I have been doing some thinking on this area for a while, but am not
sure if i am in the right direction. Please correct me where ever
neccessary.

For Qos routing across autonomous systems isn't it required that there
be a mechanism to figure out whether we have the required Qos end to
end.

Doesn't Bandwidth broker concept address the inter-domain Qos routing ?

Instead of having a centralized entity per AS as in bandwidth broker
architecture, if all the routers running BGP can generate bandwidth and
QoS related attributes for the routes generated from the AS (along with
the labels). As a result based on the policies the routers can have
multiple routes to a destination mapping to different Qos/bandwidths.

So seems like we need a well defined mechanism to export the traffic
engineering attributes of the IGP protocols to the BGP protocol and
also, the intermediate ASs when forwarding the routes received need to
figure out the QoS/bandwidth available to the next-hop and forward the
cumulative QoS/Bandwidth constrained route to other ASs.

Phani

Phanidhar Koganti
Newbridge Networks Inc.

Peter Ashwood-Smith wrote:

>
>
> Currently the MPLS working group has not addressed this subject in any
> depth although there was a draft presented in the routing area group
> today in Adelaide that started to talk about solutions.
>
> As far as I know there are basically two ways to attack this problem,
> or at least two general flavors.
>
> piecewise source routing. In this approach you compute a gateway based
> on the destination address and then do normal flat source routing to
> that gateway. Go through the gateway and repeat. In other words you
> are doing piecewise traffic engineering but letting the exterior
> gateway protocols figure out which gateway you should be going to
> next. Obviously there are problems with this approach since it puts
> everything though the same gateway. I actually helped built a
> piecewise solution like this a while ago. It has some good advantages
> in that local (at least local to an AS) repair is natural to do as are
> local modification etc.
>
> hierarchical source routing. This is what ATM does, you compute a hop
> list hierarchically against a hierarchical topology database etc. etc.
> I'm not sure this approach is appropriate for the Internet due to the
> massive size of the problem but I'm really not an ATM hierarchical
> routing guy.
>
> I would hope that the MPLS working group or the Traffic Engineering
> working group can start looking at these issues, possibly with some
> simulations of the different approaches against a set of real AS
> topologies. Some of the PNNI architects and BGP architects are active
> members  of the MPLS working group so you can be sure that it will
> cause some heated debate ... should be extremely interesting and
> challenging.
>
> Cheers,
>
> Peter
>
>