Is it possible to disable the layer 3 function on the sup720 in a cat6509E, as a step in the implementation of a secondary core we liked to have just only layer2 and not layer3, i was looking for a command "no ip routing" but couldn't find it in de ios
You are always welcome :)
Now coming to your questions "service internal" command is an engineering command and should not be used in live production network by any customer. There is no official documentation for the same.
As I mentioned in my previous post software Release 12.1(20)E and later, the support for disablement of IP routing has been removed but you mentioned you were able to do "no ip routing" on sup 720 running 12.2(18) code correct? If this is a case I am not sure why it worked may be service internal command is already enabled on the release which you are running. Not sure though. I have to dig more to find that informaion.
Your last question is very tricky and the most easy way is to check 'sh ip route" but "no ip routing" is not saved in configuration but when you issue this command we will see this command in show run as this is not the default behavior and non default commands are displayed in running config but when you reload the same it will be enable again.
So the crux of conversation is we cannot disable ip routing and to make sure there is no ruting happening just configure all physical ports as "switchport" and make sure no logical layer 3 interfaces are configured with exception of 1 interface for management purpose.
I am not sure if I am able to put my thaughts well explained.