We just bought a new 2820vn to replace our 2800. Everything used to work fine. We have a trixbox pbx, and and a lan-lan vpn set up to another site, where there's a mail server. We do not currently use the router's own VOIP facilities.

The first thing we did was to upgrade the firmware to 3.3.1.2 as it seems stable at our other site (and with improved ADSL speeds). Everything appeared to work OK, except we noticed:
- some or all of the local grandstream IP phones failed to register to the trixbox
- the trixbox failed to register on one or both of our SIP trunks (pipecall and voiptalk)
- I could not receive mail, store IMAP mail or perform any IMAP function with our server across the VPN

Everything else worked fine - download speeds were 1200KB a second, we could access the trixbox and remote server over the permanent VPN through web interface OK. The problem was just a very strange SIP registration problem, and the IMAP problem.

The Trixbox log said it was just not receiving a response. It was as if all sip registrations were being interrupted.

We checked cables, re-checked the open ports in the firewall, and could not find a problem.

We did find a workaround though: we downgraded to firmware 3.3.0.1 and everything appeared to be working absolutely fine.

Does anybody have any ideas what might have been causing this? The problem is we would like to use the newer firmware because we had better lines speeds and possibly a more stable line (it cuts off every 3-4 hours and re-syncs).

Thanks
Anthony