When I was on an ISP with CGNAT I regularly saturated the connection tracking tables which resulted in all new connections failing until some some slots were freed up.
NAT also makes it difficult to run any kind of server at home (PCP support varies) or use any kind of p2p protocol.
NAT traversal techniques don't work all the time and even when they work they may only help for coordinated connections but not for unsolicited contacts.
I've had the same experience when my ISP put me behind a CGNAT: the port table got reset every other day, and some other customer could have taken the port you wanted at that point, applications with ports hardcoded over number 2000 did not work because they could not be requested, people with PPTP VPNs could not use them anymore as GRE didn't work. Plus, enjoy getting banned from things because you share your IPv4 with plenty of strangers. The solution from the ISP was to give those who complained a "fixed IPv4 plan" for free, since that pulled you out of their IPv6+CGNAT deployment plan, at least for the moment.
> NAT also makes it difficult to run any kind of server at home (PCP support varies) or use any kind of p2p protocol.
I care about this greatly, but I'm not clear that ISP's do. On the contrary, my ISP's TOS states that I'm technically not allowed to run my own server on my home internet plan.
P2P isn't just file sharing and home servers, for example the popular PS4/Xbox/PC game "Destiny" is all serverless P2P instances. I can't imagine an ISP banning you from playing PS4 games.
I recall reading that you could make P2P connections work behind a NAT by having an external server route the connections initially. Is this not true, or does it only work in some circumstances?
When I was on an ISP with CGNAT I regularly saturated the connection tracking tables which resulted in all new connections failing until some some slots were freed up.
NAT also makes it difficult to run any kind of server at home (PCP support varies) or use any kind of p2p protocol. NAT traversal techniques don't work all the time and even when they work they may only help for coordinated connections but not for unsolicited contacts.