I have a few Cisco SPA 921 and a Quadro Epygi 4xi PXE. On a VPN connection, i connected another SPA921. I made a call, but only the external phone heard something, the phone behind the PXE heard nothing at all.
Another problem: The Quadro has an public IP. Now, if i give this IP as outbound proxy, the SPA921 can register on the quadro, but has a strange ip. I set the ip static. If the outbound proxy ip is the local ip of the quadro, everything works.