ZyXEL Communications P-335WT User Manual

P-335 Series User’s Guide

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Chapter 13 VPN Screens

In order for IPSec router A (see the figure) to receive an initiating IPSec packet from IPSec 
router B, set the NAT router to forward UDP port 500 to IPSec router A.

In cases where you want to use domain names to access Intranet servers on a remote network 
that has a DNS server, you must identify that DNS server. You cannot use DNS servers on the 
LAN or from the ISP since these DNS servers cannot resolve domain names to private IP 
addresses on the remote network

The following figure depicts an example where three VPN tunnels are created from Prestige 
A; one to branch office 2, one to branch office 3 and another to headquarters. In order to 
access computers that use private domain names on the headquarters (HQ) network, the 
Prestige at branch office 1 uses the Intranet DNS server in headquarters. The DNS server 
feature for VPN does not work with Windows 2000 or Windows XP.

Figure 87   VPN Host using Intranet DNS Server Example

Note: If you do not specify an Intranet DNS server on the remote network, then the 
VPN host must use IP addresses to access the computers on the remote network.

With aggressive negotiation mode (see Section Negotiation Mode), the Prestige identifies 
incoming SAs by ID type and content since this identifying information is not encrypted. This 
enables the Prestige to distinguish between multiple rules for SAs that connect from remote 
IPSec routers that have dynamic WAN IP addresses. Telecommuters can use separate 
passwords to simultaneously connect to the Prestige from IPSec routers with dynamic IP 
addresses (see

for a telecommuter 

configuration example).