https://en.wikipedia.org/wiki/Time_Independent_Escape_Sequen...

    DCC SEND whatever 0 0 0

This caused the DCC ALG helper in ancient Linux kernels to close the connection, as they failed to parse 0 as a valid IP address. Users connecting to IRC servers over TLS were immune, as the ALG helper in the router could not observe the traffic.

This is what breaks DCC in general -- to use DCC on IRC while connecting to the server over TLS and behind a NAT, you must instruct your client to use a specific range of ports for DCC and preforward those ports to your machine in your router, as the ALG helper cannot mark the incoming connection as RELATED (and forward it through to you) as it cannot see the outgoing command that caused the incoming connection to occur. You must also instruct your client to determine the correct external IP address to advertise, as the ALG helper will be unable to rewrite it when the router does masquerading.

My memory is a bit hazy and I don't want to look up the exact sequence, but that's close enough.

it was `{S /con/con`; my memory transposed two characters. the {S was the "system message" that AOL chatrooms used to send sounds, so that sequence of characters after a newline made your computer look for that sound. It was cool if everyone was trusted to not do the /con/con, people would have email chains with the audio files on them, like a proto-napster.