client call auto released after 15 seconds

[kuangqifu]

Hi!
My Sip phone solution is:
Sip server:Yate 6.1.0,windows 2012
Sip client A:linphone desktop,linphone web plugin
Sip client B:linphone linux
Sip server with two IP,Public network static IP:222.178.179.xxx,local ipv4:10.0.21.x
Sip client register to 222.178.179.xxx,client A and client B registed all ok.
my issue is:when i call client B from client A,after 15 seconds,the call released by client A,I notice that client A will keep alive to 10.0.21.x and send message to 10.0.21.x witch can't reach, 10.0.21.x is local IP,I need to hide local IP,only open public Ip 222.178.179.xxx to all client,I try to ysipchan.conf,but failed.
can anyone help me,please,thank you.