Re: [mpls] mpls-in-udp entropy

[Alexander Vainshtein <[e-mail]>]

Eric,
Lots of thanks for a prompt and highly informative response.

I have been actually thinking about the same thing, namely that the entropy port should be the result of some hash over the label stack.  

If this is indeed the intention of the authors, it would make sense (at least, from my point of view) of saying so in the draft. There is no need to make such a statement normative, but it would really help the readers (both implementors and operators) to understand what it is about.

Regards,
     Sasha 

________________________________________
From: Eric Rosen <[e-mail]>
Sent: Wednesday, January 15, 2014 6:35 PM
To: Alexander Vainshtein
Cc: [e-mail]
Subject: Re: mpls-in-udp entropy

(Changed subject line and trimmed cc-list.)

Sasha> I would like to understand whether this protocol can really result in
Sasha> reasonable distribution of traffic. "Reasonable" means that (a) there
Sasha> is sufficient entropy and (b) that the order in specific micro-flows
Sasha> is preserved.

I thought the intention was that the encapsulator would set the UDP source
port based upon the entropy of the packet being encapsulated.  This only
requires that the encapsulator know how to properly apply ECMP to the MPLS
packet that is being encapsulated.  That is, compute the hash that would be
used to apply ECMP to the MPLS packet, and then map from that hash to a UDP
source port.

E.g., two MPLS packets with the same entropy label would get the same UDP
source port, two MPLS packets with no entropy label but containing the same
TCP flow would get the same source port, etc.

Do you think there is a problem here?