I've just setting SIP Express Router and Mediaproxy in 1 PC. Then, I'm setting in NAT Router that only activated for MASQUERADE like this:

iptables -A POSTROUTING -s 172.17.2.0/24 -o eth1 -j MASQUERADE

NB:I assume in network 10.100.0.0/24 (eth1) as public IP and 172.17.2.0/24 as private IP.

When I calling with x-lite and activated mediaproxy service, the connection running well with 2 direction (full duplex from 10.x.x.x to 172.x.x.x conversely).But,when I stopping mediaproxy service (for proving that voice packet if pass NAT will connect half duplex or maybe broken),apparently this connection still running well with 2 direction

my question,,
why this happened?
are having trouble with mediaproxy or SIP Express Router?
i'm confusing,,

thanks very much,,
:)