The 64k Connection Myth

It’s a common misconception that you can only accept 64,000 connections per IP address and the only way around it is to add more IPs. This is absolutely false. The misconception begins with the premise that there are only so many ephemeral ports per IP. The truth is that the limit is based on the IP pair, or said another way, the client and server IPs together. A single client IP can connect to a server IP 64,000 times and so can another client IP.

From Linux Kernel Tuning for C500k.