ZyXEL 2WG Guida Utente

Chapter 15 IPSec VPN Screens

ZyWALL 2WG User’s Guide

The following examples show how multiple telecommuters can make VPN connections to a 
single ZyWALL at headquarters. The telecommuters use IPSec routers with dynamic WAN IP 
addresses. The ZyWALL at headquarters has a static public IP address.

See the following figure and table for an example configuration that allows multiple 
telecommuters (A, B and C in the figure) to use one VPN rule to simultaneously access a 
ZyWALL at headquarters (HQ in the figure). The telecommuters do not have domain names 
mapped to the WAN IP addresses of their IPSec routers. The telecommuters must all use the 
same IPSec parameters but the local IP addresses (or ranges of addresses) should not overlap. 

Adjust TCP Maximum 

Segment Size

The TCP packets are larger after the ZyWALL encrypts them for VPN. The 

ZyWALL fragments packets that are larger than a connection’s MTU 

(Maximum Transmit Unit).  
In most cases you should leave this set to Auto. The ZyWALL automatically 

sets the Maximum Segment Size (MSS) of the TCP packets that are to be 

encrypted by VPN based on the encapsulation type. 
Select Off to not adjust the MSS for the encrypted TCP packets.
If your network environment causes fragmentation issues that are affecting 

your throughput performance, you can manually set a smaller MSS for the 

TCP packets that are to be encrypted by VPN. Select User-Defined and 

specify a size from 0~1460 bytes. 0 has the ZyWALL use the auto setting.

Local and Remote IP 

Address Conflict 

Resolution

Select The Local Network to send packets destined for overlapping local 

and remote IP addresses to the local network (you can access the local 

devices but not the remote devices).
Select The Remote Network (via VPN Tunnel) to send packets destined for 

overlapping local and remote IP addresses to the remote network (you can 

access the remote devices but not the local devices.)
If the remote IPSec router also supports NAT over IPSec, it is recommended 

that you use NAT over IPSec (see 

) if 

the local and remote IP addresses overlap.
If a VPN rule’s local and remote network settings are both set to 0.0.0.0 

(any), no traffic goes through the VPN tunnel if you select The Local 

Network.

Apply

Click Apply to save your changes back to the ZyWALL.

Reset

Click Reset to begin configuring this screen afresh.

Table 92   SECURITY > VPN > Global Setting (continued)