An interesting discussion appeared over on the NANOG mailing list, based on the article, Up to 300 Megawatt Worth of Keepalive Messages to be Saved by IPv6?

This points to an original study by Haverinin, Siren and Eronen at Nokia that shows how much energy is used via "keepalive" messages sent in VoIP, Instant Messaging and other systems, in order to satisfy NAT. In order to maintain connectivity through a NAT router these systems need to keep sending messages to stop the NAT router closing the connections. With IPv6 this would no longer be necessary. It turns out the power requirements are quite significant.

There is good work happening elsewhere in Linux and elsewhere in IT, to minimise the amount of energy wasted, such as the Less Watts project. But perhaps its worth doing an audit of the protocols we use, to see what energy savings we can use?