You want the \verb command, e.g.
48-bit MAC-address: \verb+1003:AAAA:BEEF+
You can see that the argument is wrapped with +. It does not matter what character you use as long as you use a pair. So this will work too:
48-bit MAC-address: \verb21003:AAAA:BEEF2
Here the argument is wrapped with 2.
Check out Leslie Lamport's
LaTeX: A Document Preparation System