Routing isn't stateful at all, and NAT doesn't need a stateful filter, it just needs connection tracking (which is also needed for a stateful filter, if you hav

Routing isn't stateful at all, and NAT doesn't need a stateful filter, it just needs connection tracking (which is also needed for a stateful filter, if you have one). How common are stateful packet filters on home routers today? I don't really know - thanks to NAT, you can get away without for most attack scenarios nowadays, so I wouldn't be surprised if vendors don't really bother with it. But given that connection tracking doesn't seem to be that difficult with home router hardware, I would have expected stateful packet filters in home routers as a default feature early on, with everything inbound blocked by default (and then some UPnP like protocol for opening ports as needed, just without the stupid address collisions you get with NAT).