1k certainly seems absurdly small considering how much RAM routers likely have, the fact that they can use most of it, and the amount of data needed for a single connection table entry (2 bytes external port, 2 bytes internal port, 4 bytes internal IP adds up to 8 bytes per entry, even being very generous at 16 bytes including overhead, that's still only 16K --- on a device that likely has several MB if not more, and whose primary function is likely NAT.