I recently moved, and at the same time purchased a new router (Linksys E1200). Prior to the move, I had my old router set up to forward a port for SSH to servers on my LAN, and I was using DynDNS to manage the external IP address. Everything worked great.

I moved and set up the new router (unfortunately, the old one is busted so I can't try things out with it), updated the DynDNS address, and attempted to restore my port forwarding settings. No joy. SSH connections time out, and pings go unanswered.

But here's the weird part (i.e., key to the whole thing?): I can ping and SSH just fine from within this LAN. I'm not talking about the local 192.168.1.* addresses. I can actually SSH from a computer on my LAN to the DynDNS external address. It's only when the client is outside the LAN that connections are dropped.

This surely suggests a particular point of failure, but I don't know enough to figure out what it is. I can't figure out why it would make a difference where the connections originate, unless there's a filter for "trusted" IP addresses, which is perhaps just restricted to my own. No settings have been touched on the servers, and I can't find any settings suggesting this on the router admin interface. I disabled the router's SPI firewall and "Filter anonymous traffic" setting to no avail.

Has anyone heard of this behavior, and what can I do to get past it?