nice to have: ICMP translation by NAT

[adferguson]

it would be great if we wrote added support for ICMP traffic to the NAT (most importantly, the ability to ping through the NAT).

as ICMP does not use port numbers, NAT translation rewrites the "Identifier" field for ICMP query messages: http://tools.ietf.org/html/rfc5508 (NAT Behavioral Requirements for ICMP). wikipedia has a nice description of where the Identifier field is for ping packets: https://en.wikipedia.org/wiki/Ping_(networking_utility) ... unfortunately, the OpenFlow protocol does not yet support the ICMP identifier field in any revision, so rewriting will have to happen at the controller.

a bit more color is provided by http://tools.ietf.org/html/rfc3022 -- Traditional IP Network Address Translator (Traditional NAT)