I created a null0 interface in 3750, I can't see the interface in the "sh run" but I'm able to route RFC 1918 to it.
Is this normal?
I believe it is. I have just tried creating a null0 interface in our lab on
None of them showed up in config. i believe this is because it is a pseudo-interface similar to /dev/null in unix. You can always add routes that point to Null0 and the IOS will do the right thing and blackhole them.
You can also do a limited amount of config on the null0 interface but it won't take an ip address etc.