There's currently a proposal floating around to formalise a Forwarded-For header, with the same semantics as X-Forwarded-For, but with IPv6 support and perhaps more.
See: http://tools.ietf.org/html/draft-petersson-forwarded-for-00 Currently being discussed a fair amount on the HTTP WG list, starting at: http://lists.w3.org/Archives/Public/ietf-http-wg/2011AprJun/0024.html Cheers, -- Mark Nottingham m...@yahoo-inc.com