I have a firewall/router (not doing NAT).
I've googled and seen conflicting answers. It seems UDP 500 is the common one. But the others are confusing. 1701, 4500.
And some say I need to also allow gre 50, or 47, or 50 & 51.
Ok, which ports are the correct ones for IPSec/L2TP to work in a routed environment without NAT? i.e. I want to use the built in windows client to connect to a VPN behind this router/firewall.
Perhaps a good answer here is to specify which ports to open for different situations. I think this would be useful for many people.