Searched for “proxy arp” topic on Google and found a Network Lessons page for it. It is categorized under CCIE Routing and Switching but I can’t seem to actually find it by navigating through the website. I see that there is a ‘Legacy’ section under courses but when I click on that nothing happens.
I figured out the issue. The menu doesn’t support a third navigation level, which is why nothing showed up under the legacy sub-menu. I moved it to the main menu so you can see all the old courses again: