Subject: AW: your mail

From: Hummel Heinrich <[email-masked]>
Date: Tue, 2 Jul 2002 16:25:37 +0200

It  gets weirder  and weirder: The MPLS WG invents a label stack, but does not care at all that any of the
deeper nested labels may ever be signalled/carried by means of a Label-TLV/object (no public comments to my
Hierarchical LSPs, draft-hummel-mpls-hierarchical-lsp-01.txt).

However it is ok, to "steal" the deepest nested label and call it "VC-label" for indexing
some VRF at some remote PE. Furthermore it is ok, to "steal" the very same label for hashing.

Independent from what is clean and what is quick&dirty, I cannot detect any sense in giving a hash-meaning to the bottom label at all.

Heinrich Hummel
Siemens

-----Ursprüngliche Nachricht-----
Von: Eric Rosen [mailto:[email-masked]]
Gesendet: Dienstag, 2. Juli 2002 16:06
An: Shahram Davari
Cc: 'Eric Osborne'; George Sheng; [email-masked]; [email-masked]
Betreff: Re: your mail 

Shahram> To do ECMP, you need to  assign hashed values to egress ports. This
Shahram> assignment is the hash state that I said you need.  

A hash is  a function that maps  some sequence of octets into  a sequence of
integers.  If you want to split  traffic over six paths, while ensuring that
all packets  with the  same bottom label  travel the  same path, you  need a
function that maps  a 20 bit quantity  into a number from 1-6.   There is no
need to maintain state of any kind.

---

From: Eric Rosen <[email-masked]>
Date: Tue, 02 Jul 2002 10:50:09 -0400

Heinrich> Independent from what  is clean and what is  quick&dirty, I cannot
Heinrich> detect any sense  in giving a hash-meaning to  the bottom label at
Heinrich> all.  

The only  purpose of the loadbalancing  hash is to reduce  the likelihood of
packets from the same end-to-end stream being sent on different paths, while
also not requiring  too many unrelated packets to be sent  on the same path.
Packets from  the same end-to-end stream  will tend to have  the same bottom
label,  and  at the  bottom  of  the stack  there  hasn't  been overly  much
aggregation.  So the bottom label seems  like the right thing to look at for
this  purpose.  In both  the L2VPN  and L3VPN  applications, this  works out
pretty well.

---

From: Eric Osborne <[email-masked]>
Date: Tue, 2 Jul 2002 13:32:09 -0400

On Tue, Jul 02, 2002 at 04:25:37PM +0200, Hummel Heinrich wrote:
> some VRF at some remote PE. 

This is not theft; it's using the labels as they were designed.  How
is using the bottommost label as a VC-labe/VPN label/whatever
"stealing"?  You seem to be attacking the very idea of label stacking,
which is a pretty useful concept.

> Furthermore it is ok, to "steal" the very same label for hashing.
> 

What about IP router vendors that do load-balancing based on L4/L5
information like protocol type and port numbers?  Is that stealing?

eric