ZyXEL Communications ISG50 User Manual

Chapter 6 Configuration Basics

ISG50 User’s Guide

Policy Routes: These are the user-configured policy routes. Configure policy routes to send 
packets through the appropriate interface or VPN tunnel. See 

 for more on 

policy routes.

1 to 1 and Many 1 to 1 NAT: These are the 1 to 1 NAT and many 1 to 1 NAT rules. If a private 
network server will initiate sessions to the outside clients, create a 1 to 1 NAT entry to have the 
ISG50 translate the source IP address of the server’s outgoing traffic to the same public IP address 
that the outside clients use to access the server. A many 1 to 1 NAT entry works like multiple 1 to 1 
NAT rules. It maps a range of private network servers that will initiate sessions to the outside 
clients to a range of public IP addresses. See 

 for more.

Auto VPN Policy: The ISG50 automatically creates these routing entries for the VPN rules. 
Disabling the IPSec VPN feature’s Use Policy Route to control dynamic IPSec rules option 
moves the routes for dynamic IPSec rules up above the policy routes (see 

). 

Static and Dynamic Routes: This section contains the user-configured static routes and the 
dynamic routing information learned from other routers through RIP and OSPF. See 

 for more information.

Default WAN Trunk: For any traffic coming in through an internal interface, if it does not match 
any of the other routing entries, the ISG50 forwards it through the default WAN trunk. See 

 for how to select which trunk the ISG50 uses as the default. 

Main Routing Table: The default WAN trunk is expected to be used for any traffic that did not 
match any earlier routing entries.

The checking flow is from top to bottom. As soon as the packets match an entry in one of the 
sections, the ISG50 stops checking the packets against the NAT table and moves on to bandwidth 
management.

NAT Table Checking Flow