Thanks Dave.

I do not have any proxy servers running right now, so that is why the port forward issue is a bit perplexing. I feel like there is a firewall issue on one side blocking traffic on the tunnel, but that isn't exactly scientific.

Given the issue, I'm not entirely sure which tcpdump path I should take. I ran ping tests and pings to hosts behind the tunnel at site B are actually received by the local router.

Some site info:

Site A - subnet 192.168.3.0/24
Site B - subnet 192.168.10.0/24

Here is what I did so far:

Fired up tcpdump -i <interface> icmp[icmptype]=icmp-echo on all four of my ClearOS interfaces (internal and external on both systems)

Pinged from a client behind ClearOS A to a client behind ClearOS B
I see the pings showing up on the appropriate interfaces, but I get timeouts on the ping

Pinged from a client behind ClearOS B to a client behind ClearOS A
I see the exact same tcpdump behavior (in reverse this time for obvious reasons) but the pings actually return.

I'm open for any/all other tests I can run here to determine what might be going on. The tunnel is up and no errors in the logs, so this seems to be firewall related. Again, I'm guessing a bit here.