Yeah, my apologies. You're indeed correct. I was incorrectly assuming that all NATs dynamically assign a new external port per destination IP-port tuple. As th

Yeah, my apologies. You're indeed correct. I was incorrectly assuming that all NATs dynamically assign a new external port per destination IP-port tuple. As this is what I've observed in practice. However, it looks as though many believe this only occurs for Symmetric NATs, and never Cone NATs. It seems the common terminology just isn't nuanced enough to explain what's really going on. Wikipedia[1] actually has an interesting paragraph regarding terminology: > Many NAT implementations combine these types, and it is, therefore, better to refer to specific individual NAT behaviors instead of using the Cone/Symmetric terminology. RFC 4787 attempts to alleviate confusion by introducing standardized terminology for observed behaviors. [...] Specifically, most NATs combine symmetric NAT for outgoing connections with static port mapping, where incoming packets addressed to the external address and port are redirected to a specific internal address and port. The CGNATs I've encountered, which perhaps aren't representative, are mobile network CGNATs. By observation they were behaving like Restricted (either Address or Port) Cone NATs for inbound packets, but like Symmetric NATs for outbound packets. Hence, the source of my confusion in believing all Cone NATs exhibited this behaviour. EDIT: I'm admittedly poor with the terminology as it's been years since I read the RFCs. I was only now able to express the above after doing a lot of refresher reading. I was coming at this based on experience implementing custom UDP P2P protocols, where I mostly just care about the worst case scenario; and had evidently assumed it more common than it is. [1] https://en.wikipedia.org/wiki/Network_address_translation#Methods_of_translation https://en.wikipedia.org/wiki/Network_address_translation#Me...