Subject: [mpls] Entropy size in draft-decraene-mpls-slid-encoded-entropy-label-id

From: "Joel M. Halpern" <[email-masked]>
Date: Thu, 31 Mar 2022 12:07:43 -0400

I am trying to understand if the opposing forces for field size in this 
draft mesh weell or badly.

As I read the draft, the number of bits being used for what the draft 
calls the slice ID has to be sufficient to represent the number of 
distinct slice-like-things (I think these are roughly what Bestbaer 
calls slice aggregates) that the network forwarding has to be aware of?
While that is a much smaller number than the number of external network 
slices, it still takes 8 or 10 bits on many networks?

Side note:  If it is actually intended to number the external network 
slice instances rather than IETF network slices or bestbar slice 
aggregates, then significantly more bits will be needed.

At the same time, we need enough bits left over for effective entropy 
operation within an identified slice-like collection.  While some of 
those will have only a few flows, some of them will have a lot. 
Still,we could hash down to a small field.  But...  this seems likely to 
reduce the efficacy of ECMP within the slice-like-collection.  I do not 
see any discussion of this in the draft.  Has it been analysed for 
sufficiency?

Yours,
Joel