Service Internal

I took the advice of Stretch from PacketLife and decided to research the various lines of our firm's routers configurations. So what happens first command I research I find it pretty hard to find out what it does. The command I was researching was service internal. After some searching round the web I found that it if you apply it in global configuration mode it causes some previously hidden commands to show up.

If anyone else has any knowledge on this command then please let me know.