I can confirm that the FIOS Quantum Gate router G1100 (Firmware 01.03.02.03) absolutely has an issue with port forwarding for L2TP (UDP ports 500,1701, 4500, GRE, ESP, AH) as has been reported in this older forum (»
[Networking] Quantum G1100 Gateway VPN Issue)
What I know is that enabling port forwarding of (UDP ports 500,1701, 4500) to an L2TP server (in my case a Synology DS214play running DSM 6.0.1) on my network will sometimes work very briefly and then will just stop working after a few minutes.
Some other observations to be aware:
- This is only a problem on the FIOS Quantum Gateway router G1100. I had the Actiontec router previously and this was not an issue on that router.
- Make sure "Back to my Mac" service is off on all Macs and Airport devices on your local network. This service stealthily uses port 4500 which will interfere with the L2TP ports.
- Only L2TP ports seem to be affected as OpenVPN (UDP 1194) and PPTP VPN (TCP 1723) services work flawlessly all the time.
- Enabling DMZ on my Synology server (L2TP server) will allow the service to work but leaving my server on DMZ is not a comfortable option for me.
I have been in touch with level 2 support at Verizon FIOS and sadly they are of no help and start spouting crap like - we do not support VPN. Blah blah blah. Well then why is there a preset Port Forwarding Rules for L2TP? And why does OpenVPN and PPTP work consistently? And why would they deliberately block one of the more secure VPN method while leaving one of the less secure VPN (PPTP) open and working?
Looking for anyone who has resolved this issue or has a viable workaround. I am thinking of enabling DMZ on a second router with double NAT but frankly this is silly to have to do that when this should just work.