Limit access to backoffice

What options are available to limit access to sitename.com/litium?
We would like the site to return a 404 if the backoffice is accessed from anywhere except our office.

Thank you.
/Peter

Litium version: [6]

For one of our older projects, we have set up an IP-block in IIS. So that only certain IP-addresses can access that, all others get 404. It works for this customer, as everyone that needs access to backoffice, work from an office with shared IP.

Firewall rule or iis url rewrite rule is usually used to solve this for us.

Great! Thank you.