I have 2 sites with zeroshell routers (v 3.0) connected via site-to-site vpn. Site one there is sip server, site two there are sip clients. I have configured static routes and everything works fine until there is vpn reconnection (because of isp etc.). Then every service reconnects fine except sip. Sip get some very strange behavior. Zeroshell route sip traffic through vpn tunnel, but with source address of external interface (dumped on vpn interface). It is definitely zeroshell issue because when i restart client sip pc it will not help. Helps only change of IP address on client side. But after some time (about 8-12 hours), it can reconnect with same ip address. It is not dhcp issue because I tested it on static and dhcp configured clients. When I reboot zeroshell it helps also. So I think there is some session on zeroshell, which breaks with vpn reconnection. But udp traffic should not have sessions as I know. Strange is that only sip traffic is affected and only hosts which are actually connected during vpn reconnection.
I would be very grateful for every idea.