\_ I just did a nmap on one of my routers (cisco 2500) and there is
\_ one line that I cannot explain:
\_ 
\_ 6001	open	tcp	X11:1
\_ 
\_ What is this? How can I close this if not needed?

Heh....

6000-6009 are classically ports for X11 displays, 6001 is :1 (hence,
the X11:1).

What your router is doing with X11 is a good question.  

There is a slim chance it could be an xfontserver, but then what is
your router doing with an xfontserver?

David