Subject: RE: your mail

From: "Gray, Eric" <[email-masked]>
Date: Mon, 22 Jul 2002 17:06:17 -0400

Shahram,

	There is nothing to be fearful, uncertain or
doubtful about here.

	If an implementation can handle up to N labels,
then it can use either the bottom-of-stack label or
the Nth label for a hash key.  With respect to flows,
this will be consistent.  It will also tend to give
the greatest degree of entropy in hashing possible
for a specific labeled packet.  It doesn't guarantee
even distribution any worse than any other 'guess'.

	Use of the IP header as well is a) unnecessary,
b) unhelpful and c) not a good idea.

Eric W. Gray
Systems Architect
Celox Networks, Inc.
[email-masked]
508 305 7214

-----Original Message-----
From: Shahram Davari [mailto:[email-masked]] 
Sent: Monday, July 22, 2002 4:48 PM
To: [email-masked]'
Cc: 'Giles Heron'; [email-masked]; [email-masked]; [email-masked]
Subject: RE: your mail 

Hi Eric,

If I understand you correctly, what you are saying is that assume a number
such as "N", and hash the Nth label, regardless of whether it is the 
real bottom-most label (i.e. with S=1) or not. If so then:

1) How do you know that at least N labels exist in all packets?
2) The Nth label can not identify a flow by itself, rather you need to hash
the whole label stack from the top, up to the Nth label, in order to
identify a flow.
3) I have heard that some implementations hash the IP header too? How does
that fit in to your model? How do you know that the payload is IP? And don't
you need to find the real bottom of stack (S=1) in order to include the IP
header in the hash?

Yours,
-Shahram

> -----Original Message-----
> From: Eric Rosen [mailto:[email-masked]]
> Sent: Monday, July 22, 2002 3:15 PM
> To: Shahram Davari
> Cc: 'Giles Heron'; [email-masked]; [email-masked];
> [email-masked]
> Subject: Re: your mail 
> 
> 
> 
> Shahram> "Deep" or "not deep"  you need potentially unlimited 
> packet parsing
> Shahram> (uo to  MTU size), since as you  said the number of  
> labels are not
> Shahram> limited to 2. 
> 
> To  the MTU  size?   That would  be for  the  case where  the 
> entire  packet
> contains the MPLS label stack and there is no payload?
> 
> As has been made  clear repeatedly, you can hash on any  
> label, you just get
> more fine-grained load balancing the  further down you go.  
> So generally you
> would look  at the  bottom-most label  that you can  easily 
> see,  given your
> particular forwarding architecture. 
> 
> 
> 
>