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

From: "Hitesh Kulkarni" <[email-masked]>
Date: Sun, 24 Nov 2002 13:23:37 -0800

Sorry for opening this old thread again after a long time..

David,

In a few current or next gen boxes hw genarally has capability to look into 
the payload even for labelled traffic for load distribution purposes on aggr 
links etc right??

with regards,
hkulk

>From: David Charlap <[email-masked]>
>To: IETF MPLS List <[email-masked]>
>Subject: Re: Does a labeled packet go through "Packet Filtering/Policy  
>Routing/Filter Based Forwarding"?
>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: David Charlap <[email-masked]>
Date: Mon, 25 Nov 2002 10:11:22 -0500

Hitesh Kulkarni wrote:
> 
> In a few current or next gen boxes hw genarally has capability to look 
> into the payload even for labelled traffic for load distribution 
> purposes on aggr links etc right??

Was there a question in here?  Asking a working group about whether 
somebody has implemented something in hardware isn't exactly a useful 
question.  You may be better off asking groups that deal with users of 
protocols, or developers of hardware.

I think you meant to ask whether hadware with this capability may use it 
for forwarding labeled traffic.

My answer is that it can use whatever it wants, but it would be a dumb 
idea.  Unless you want your hardware to snoop RSVP LABEL_REQUEST objects 
and also monitor for Martini-type labels in the stack, _and_ have 
configured knowledge about any exceptions, your hardware won't always 
guess correctly about what the LSP's payload is.  If it's not the type 
you think it is, then you will be reading garbage values, and you'll be 
making incorrect decisions based on that garbage.

If you think a packet carries an IP payload when it's really AppleTalk, 
or IPX, or Ethernet frames, or raw voice data, or something else, and 
you start doing load-balancing forwarding calculations based on what you 
think you find in there, you're going to break the traffic.

-- David