[TheDopp]

It's TECHNICALLY possible to cause a Nat Overflow (technically a stack overflow as there is no maximum connections for NAT on older devices), but you're looking at about 10000-15000 unique connections within the default 500ms timeout and assuming it's a cheap enough router not to have either Nat Overload, or a stack drop (where it forcefully purges the table if it hits a certain number).

This would be an insane feat, though, as even some of the most famously large DDoS attacks have been limited to about 1000 machines, and we're talking about getting about 2-5 unique connections PER MILLISECOND over a home connection.

Most ISP's won't allow you to have that many active connections in that short amount of time (most of them wouldn't even forward that many due to local backbone limitations), and the router would have to be responding to them in order for the connections to bypass delayed binding.

In other words, case closed, his router was probably just old, dusty and overheating which caused it to crash and the CSR at his ISP just saw an open UDP connection to a game server, or the porn torrent he had going as "an attack".