Subject: RE: Finding the Egress Point in the MPSL Domain for the specific Destination

From: "Manish R. Shah." <[email-masked]>
Date: Tue, 25 Apr 2000 10:55:24 +0530

Hi !!!

Once the LSP's are created, the ingress router looks for the matching FEC, and attaches 
a label corresponding to that FEC on to the data packet. Further forwarding is done using
the label switching. 

In an MPLS domain the LDP has already taken care of mapping 
FEC's with the incoming and outgoing Labels and efficient distribution of Labels.

Look at the following draft for furthur details.  draft-ietf-mpls-ldp-06.txt 

Cheers !!!

Manish R. Shah.
Senior Software Engineer,
Future Software Pvt Ltd.
480-481, Anna Salai, Nandanam
Chennai 600035.
Phone: +91-(44)-433-0550 Xten 294.

-----Original Message-----
From:	Neetu Gupta [SMTP:[email-masked]]
Sent:	Tuesday, April 25, 2000 10:28 AM
To:	[email-masked]
Subject:	Finding the Egress Point in the MPSL Domain for the specific Destination

Hello,
    Suppose the LSPs are created among the Edge Routers in the MPLS
Domain with specific class of services. Now the data packet comes at the
Ingress LER, the IP Header contains the Destination Address and TOS
byte.

Since there are labels to Egress Router, to which Egress LER the data
packet will be forwarded that will route to the Destination?

I've heard of the draft that specifies how to treat LSP tunnel end node
like LSP egress edge as next node for route calculations.
Please give some reference.
Neetu

---

From: Neetu Gupta <[email-masked]>
Date: Tue, 25 Apr 2000 11:11:33 +0530

Thanx for the Response:

But, actually the Signaling protocol that we are using is RSVP. We create LSPs initially for
the Class of Services specified in the Service Level Agreements for the Differentiated
Signaling case. Service Level Agreement also specifies what will the Ingress point for the
LSP. Also, all the Edge Routers in the MPLS domain are preconfigured. So the LSPs are created
from the Ingress point to every Edge Router. Now the data packet for the destination outside
the MPLS domain comes, how can we find out which Egress LER will route to the Destination,
because at Ingress point we have label to Egress LER and not the Destination in the Switching
Table

-neetu

---

From: Bora Akyol <[email-masked]>
Date: Tue, 25 Apr 2000 17:39:10 -0700

I presume you are not familiar with how MPLS is actually used in providers 
networks.

FEC to LSP binding is almost historical now.

Bora

---

From: Jeremy Lawrence <[email-masked]>
Date: Wed, 26 Apr 2000 18:47:13 +1000

At 17:39 04/25/2000 -0700, Bora Akyol wrote:
>I presume you are not familiar with how MPLS is actually used in providers networks.

I presume you are not familiar with how MPLS is actually used in providers'
ATM networks. :)

>FEC to LSP binding is almost historical now.

That's arguably true in router-based networks, because of the
predominance of TE as an application of MPLS in those networks.
However, FEC to LSP binding is very much alive in ATM MPLS
networks. Also, at least one MPLS-based VPN scheme relies on
hop-by-hop routed MPLS (which may, in turn, be over-ridden by
TE) in network cores of any type.

Regards,

Jeremy Larence

---

From: [email-masked] (David Wilder)
Date: Wed, 26 Apr 2000 11:13:29 -0400 (EDT)

Hello,

I don't understand why you say that FEC to LSP bindings would be 'historical'
in router-based networks.  Would one of you expand on that for me?

Thanks,

Dave

---

From: Narin Suphasindhu <[email-masked]>
Date: Wed, 26 Apr 2000 13:07:33 -0400 (EDT)

:>LSP. Also, all the Edge Routers in the MPLS domain are preconfigured.
:>So the LSPs are created from the Ingress point to every Edge Router.
:>Now the data packet for the destination outside the MPLS domain comes,
:>how can we find out which Egress LER will route to the Destination,
:>because at Ingress point we have label to Egress LER and not the
:>Destination in the Switching Table

Hi Neetu,

If I understand the question correctly, at the Ingress LER, you'd run BGP
to map destination prefixes to Egress LER.  Hence, destination prefixes to
LSPs.

Cheers,
-Narin

---

From: Bora Akyol <[email-masked]>
Date: Wed, 26 Apr 2000 10:08:06 -0700

I would urge you to look at what other network operators/vendors are 
deploying in their networks.

Specifically, what people are doing is running a modified version of the 
IGPs that use an SPF that ALWAYS prefers MPLS LSPs if there is an LSP that 
originates from the router running the SPF to the router that the SPF is 
trying to find a shortest path to. Then this new found route (LSP) is 
inserted directly into the route table.

So you get automatic LSP to FEC binding which does not need to be signaled 
by the Label Distribution protocols (RSVP, CR-LDP, LDP). IMHO, this is nice.

Therefore, I believe that explicitly specifying the FEC and LSP binding is 
only justified in very unique situations; otherwise, it is history.

Henk Smit et al, submitted an ID about this months ago (expired by now). I 
guess it did not quite get read.

Bora Akyol
Pluris (http://www.pluris.com)

---

From: Eric Rosen <[email-masked]>
Date: Wed, 26 Apr 2000 14:00:04 -0400

Bora> Specifically, what people are doing ...

Generally, when a message begins like  this, it goes on to mention something
that some people are doing some  of the time, and then makes inferences that
would only be valid if that is what everyone were doing all of the time.

---

From: Bora Akyol <[email-masked]>
Date: Wed, 26 Apr 2000 13:52:07 -0700

You are right,

I did not think about the ATM case (I should have been more specific, 
apologies extended), but I do not understand the difference between having 
MPLS LSP over POS vs MPLS LSP over ATM as long as either end of the LSP 
understands IP; i.e. what is the significance to the IP router of having 
MPLS over ATM vs MPLS over POS LSP? Or is there an ATM switch at one end of 
the LSP that does not have a routing protocol running and uses a 
lookup/classification table for IP to LSP mapping (ouch).

Thanks for catch.

Bora

---

From: Bora Akyol <[email-masked]>
Date: Wed, 26 Apr 2000 13:06:36 -0700

Eric

No need to insult my credibility.

The MPLS deployments that I have seen in the Tier 1 service provider market 
do use the modified IGP SPF and do not use the explicit LSP-to-FEC binding. 
Not only that but both your company's documentation and another router 
vendor's documentation suggest exactly what I wrote as the way to do TE.

So what this leaves is the use of LDP for VPNs that use FEC to LSP binding.

Maybe you should review your company's documentation and check with your 
customers.

Bora