Which of the following domain name extensions is used for gateways and administrative hosts?

The .net extension was originally intended for network infrastructure such as gateways and administrative hosts.

The .gov extension is reserved for government bodies, not network infrastructure.

The .mil extension is reserved for military organisations.

The .org extension was intended for non-profit and other organisations.

These are all generic top-level domains distinguished by their intended user type.

In practice .net is now open for general registration by anyone.