Hi Here's is my setup. It's not that complicated. 172.168.128.0/24 subnet FS <-------------------------------------------> IPCOP Firewall | | 10.10.0.0/24 subnet Extension 1000 <--------------------------------->| |<-------------------------------------------- Extension 1001 (172.168.128.188) (10.10.0.170) Firewall is set to allow all UDP traffic in the port rane 1024-65000 between these two subnets. Both 1000 and 1001 register successfully with FS. I can make outgoing calls (using vitelity) using both. I can call 1000 from 1001 ok. However, calling 1001 from 1000 doesn't work. It goes right to 1001's VM. It's as if FS doesn't know 1001 is registered. My config is almost same as what comes with vanilla FS install (except I defined outgoing vitelity and 1000.xml and 1001.xml extensions). Any obvious config I'm missing? Thanks in advance.