While I realise that it's a parody on "One does not simply walk into Mordor!" (I believe it's a statement made by Boromir), I was wondering where that particular meme comes from. The connection (no pun intended) between Mordor and the Telnet Protocol is just so arbitrary.
According to Know Your Meme, the "One Does Not Simply X Into Mordor" snowclone/image macro/meme seems to have originated in the Something Awful forums in 2004. Lots of great examples of other ones (including puns) on that page.
Yes, it is arbitrary. That's what happens with memes. It started with "one does not simply walk into Mordor," as you said, then various people just posted "one does not simply walk into x" and "one does not simply x into Mordor" for all x they could think of, and someone just happened to put telnet into it. There's nothing deeper about it, it's just the nature of memes.
It might be related to [the custom of naming computers after LotR characters
and Mordor might then be the name of a Network that is claimed to be difficult to access without permission.
However, Telnet is also used for MUDs, and indeed there is at least one LotR MUD with telnet access. So, this might refer to a MUD and a difficulty that is most likely so high that playing for the good side one could not simply get to Mordor. However I'm just speculating here, maybe someone who has played LotR MUDs can confirm/falsify this.
I have not read the LOTRs books, but I have come across this meme on our servers. I have noticed UNIX servers named mordor (and gondor too) and directory paths such as /home/mordor.
Once some log files I needed were stored in one of these, but when I tried to access them I found out that I lacked the required permissions. Then of course, someone said "One does not simply cd (change directory) into mordor".
If one tries to telnet into a server named mordor, one usually gets the smug response "One does not simply telnet into mordor. One uses SSH."