said by HELLFIRE:May help to know the make/model of equipment you're using on both ends
Server 2008 for the server and clients are Windows7/8.1
said by HELLFIRE:what troubleshooting you've done so far, besides simply "believ(ing) ESP packets are getting lost."
I did a Wireshark packet capture and it was dropping packets. I'm pretty sure it was ESP packets that were being lost.
I can ping the server, and all other packets make it there just fine.
said by HELLFIRE:I'd also confirm the particular carrier's support of IPv6, as I've heard anecdotally not all fully support IPv6
Why does this not surprise me.