Dup Loop
/d[y]oop loop/
(also 'dupe loop') [FidoNet] n. An
incorrectly configured system or network gateway may propagate
duplicate messages on one or more echoes, with different
identification information that renders dup killers
ineffective. If such a duplicate message eventually reaches a
system through which it has already passed (with the original
identification information), all systems passed on the way back to
that system are said to be involved in a dup loop.
More Jargon: