ZyXEL Communications P-2302HWUDL-P1 Series User Manual

 Chapter 8 NAT

P-2302HWUDL-P1 Series User’s Guide

Some NAT routers may include a SIP Application Layer Gateway (ALG). A SIP ALG allows 
SIP calls to pass through NAT by examining and translating IP addresses embedded in the 
data stream. When the ZyXEL Device registers with the SIP register server, the SIP ALG 
translates the ZyXEL Device’s private IP address inside the SIP data stream to a public IP 
address. You do not need to use STUN or an outbound proxy (see 

your ZyXEL Device is behind a SIP ALG.

Use this screen to enable and disable NAT and to allocate memory for NAT and firewall rules. 
To access this screen, click Network > NAT > General.

Figure 69   Network > NAT > General

Each field is described in the following table.

Table 55   Network > NAT > General

NAT Setup

Enable Network 

Address 

Translation

Select this if you want to use port forwarding, trigger ports, or any of the ALG.

Max NAT/Firewall 

Session Per User

When computers use peer to peer applications, such as file sharing 

applications, they may use a large number of NAT sessions.

 If you do not 

limit the number of NAT sessions a single client can establish, this can result in all 

of the available NAT sessions being used. In this case, no additional NAT 

sessions can be established, and users may not be able to access the Internet.  
Each NAT session establishes a corresponding firewall session. Use this field to 

limit the number of NAT/firewall sessions each client computer can establish 

through the ZyXEL Device. 
If your network has a small number of clients using peer to peer applications, you 

can raise this number to ensure that their performance is not degraded by the 

number of NAT sessions they can establish. If your network has a large number of 

users using peer to peer applications, you can lower this number to ensure no 

single client is using all of the available NAT sessions.  

Apply

Click this to save your changes and to apply them to the ZyXEL Device.

Cancel

Click this to set every field in this screen to its last-saved value.