how many bits of entropy do we need for load balancing?

["Pascal Thubert \(pthubert\) via NANOG" <nanog () nanog org>]

Dear all:

How many bits of entropy do we need for (ECMP) load balancing in the core?
This question has kept coming up regularly in many discussions and drafts at the IETF.

The IPv6 flow label is 20 bits but hardware implementations do their balancing only on a subset of that, e.g. 12 or 16 
bits.

There are drafts for MPLS, BIER etc.. that provide their own entropy bit fields of various sizes.
I traced to a 6MAN discussion at IETF 78 a claim that 10 or 11 bits were enough.

Did someone do the actual exercise? It would be neat to align the IETF specs in the making to whatever truth may be 
established in the core.

Keep safe,

Pascal