ZyXEL Communications NXC5200 User Manual page 550

Chapter 39 Troubleshooting
You can set the NXC's firewall to permit the use of asymmetrical route topology on
the network (so it does not reset the connection) although this is not
recommended since allowing asymmetrical routes may let traffic from the WAN go
directly to the LAN without passing through the NXC. A better solution is to use
virtual interfaces to put the NXC and the backup gateway on separate subnets.
I changed the LAN IP address and can no longer access the Internet.
The NXC automatically updates address objects based on an interface's IP
address, subnet, or gateway if the interface's IP address settings change.
However, you need to manually edit any address objects for your LAN that are not
based on the interface.
I configured application patrol to allow and manage access to a specific service
but access is blocked.
• If you want to use a service, make sure both the firewall and application patrol
allow the service's packets to go through the NXC.
• The NXC checks firewall rules before it checks application patrol rules for traffic
going through the NXC.
I configured application patrol to block use of a specific service but a few packet's
still get through.
The NXC allows the first eight packets to go through the firewall, regardless of the
application patrol policy for the application. The NXC examines these first eight
packets to identify the application.
I configured policy routes to manage the bandwidth of TCP and UDP traffic but the
bandwidth management is not being applied properly.
It is recommended to use application patrol instead of policy routes to manage the
bandwidth of TCP and UDP traffic.
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NXC5200 User's Guide