Subject: RE: your mail

From: Shahram Davari <[email-masked]>
Date: Tue, 23 Jul 2002 07:04:12 -0700

Thanks Eric,

Your response seems reasonable. However, I have heard that
some implementation hash the label stack, up to the Nth
label or bottom-label (if the stack has less than N labels).
Does that mean that the hashing algorithm should operate on a 
variable length input? And if so does such an algorithm exist?

Yours,
-Shahram

> -----Original Message-----
> From: Gray, Eric [mailto:[email-masked]]
> Sent: Monday, July 22, 2002 5:06 PM
> To: Shahram Davari; [email-masked]'
> Cc: [email-masked]
> Subject: RE: your mail 
> 
> 
> 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. 
> > 
> > 
> > 
> > 
>