21 Oct, 2011, Scandum wrote in the 81st comment:
Votes: 0
I've gone ahead and added a PROXY flag to the MTTS standard, which allows proxy clients to identify themselves as proxies. I also added a Proxies subsection to the MTTS standard that details how to exchange IP address information over the NEW-ENVIRON telnet option.

The reason I picked NEW-ENVIRON is because the implementation burden is small compared to fully supporting GMCP or MSDP, and that MSDP was never intended to be used for this purpose.