ZyXEL Communications ZyWALL USG Series Application Note page 179

4.7.2.4 Set Up a DMZ to LAN Firewall Rule for SIP
The firewall blocks traffic from the DMZ zone to the LAN1 zone by default so you need to create a
firewall rule to allow the IPPBX to send SIP traffic to the SIP clients on the LAN.
Click Configuration > Firewall > Add. Set the From field as DMZ and the To field as LAN1. Set the
1
Destination to the IPPBX's DMZ IP address object (DMZ_SIP). Set the
Leave the Access field to allow and click OK.
4.7.3 What Can Go Wrong
• The ZyWALL checks the firewall rules in order and applies the first firewall rule the traffic matches.
If traffic matches a rule that comes earlier in the list, it may be unexpectedly blocked.
• The ZyWALL does not apply the firewall rule. The ZyWALL only apply's a zone's rules to the
interfaces that belong to the zone. Make sure the WAN interface is assigned to WAN zone.
to IPPBX_DMZ.
Source