I have a Linux gateway with kernel 2.6.39 connected to a Cisco ASA 5500 with vpnc. I'm using iptables with masquerading and forwarding to give the LAN access to the tun0 device connected to the VPN.
My Cisco IP Phone 7941 can connect to the call manager but I only get one way audio when a call is established. tcpdump -i any on my LAN gateway shows the rtp traffic originating on my phone lan IP, then being NAT'ed to the tun0 address, and finally going over my ext interface encapsulated in esp. tcpdump on the tun0 interface only shows traffic going to the rtp destination from the tun0 src IP. From my LAN's viewpoint, outbound rtp traffic is being translated correctly.
However, the asa syslog shows my lan IP address - not my tun0 address - being dropped on the remote VPN server. Any suggestions how to proceed with troubleshooting?