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ZyWALL USG 50 User’s Guide

Use the firewall to block or allow services that use static port numbers. Use 
application patrol (see 

) to control services using flexible/

dynamic port numbers. The firewall can also limit the number of user sessions.

This figure shows the ZyWALL’s default firewall rules in action and demonstrates 
how stateful inspection works. User 1 can initiate a Telnet session from within the 
LAN1 zone and responses to this request are allowed. However, other Telnet traffic 
initiated from the WAN or DMZ zone and destined for the LAN1 zone is blocked. 
Communications between the WAN and the DMZ zones are allowed. The firewall 
allows VPN traffic between any of the networks.

Figure 214   Default Firewall Action

 

   

• Use  the  Firewall screens (

) to enable or disable the 

firewall and asymmetrical routes, and manage and configure firewall rules. 

• Use  the  Session Limit screens (see 

) to limit the 

number of concurrent NAT/firewall sessions a client can use.