Subject: Does a labeled packet go through "Packet Filtering/Policy Routing/Filter Based Forwarding"?

From: Sachin Kalra <[email-masked]>
Date: Thu, 24 Oct 2002 12:02:18 -0400

Dear MPLS Community:

A quick question. Does a labeled packet go through "Packet Filtering/Policy 
Routing/Filter Based Forwarding"?

Thanks,
Sachin Kalra

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From: David Charlap <[email-masked]>
Date: Thu, 24 Oct 2002 12:42:00 -0400

Sachin Kalra wrote:
> 
> A quick question. Does a labeled packet go through "Packet 
> Filtering/Policy Routing/Filter Based Forwarding"?

What would you have it filter on?  A transit router should not make 
forwarding decisions based on anything other than the topmost label.  If 
you start drilling down into the packet payload to make these decisions, 
then why bother using MPLS at all?

One of the key reasons for MPLS these days is the ability to optimize 
traffic engineering.  You will decide your route through the network 
when you set up the LSP.  The node at the LSP's ingress will decide 
which packets to forward into which LSP.  Once that decision is made, 
the packets should not be examined again until they emerge from the 
other end of the LSP.

-- David

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From: "chetan kumar s" <[email-masked]>
Date: Fri, 25 Oct 2002 12:03:39 +0530 (IST)

> Routing/Filter Based Forwarding"?

Yes, the labeled packets go through "Packet Filtering/Policy
Routing/Filter Based Forwarding". But unlike regular IP forwarding that
requires these rules to be applied at every nodes, in case of MPLS these
rules can be applied at one single node. And rest is done by the MPLS
network.
	In MPLS each packet is assigned to an FEC (Forward Equivalent
Class). Once this is done, only at the ingress, the packets are labled
and rest of the network identifies the packet based on this label. One can
assign packet to a FEC based on IP dest address combined
with Filtering/Policy based rules.

Thanks
Chetan S

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