ZyWALL 5/35/70 Series User’s Guide

The following table describes the labels in this screen.

Table 149 System DNS: Insert Name Server Record

LABEL

DESCRIPTION

 

 

Domain Zone

This field is optional.

 

A domain zone is a fully qualified domain name without the host. For example,

 

zyxel.com.tw is the domain zone for the www.zyxel.com.tw fully qualified domain

 

name. For example, whenever the ZyWALL receives needs to resolve a

 

zyxel.com.tw domain name, it can send a query to the recorded name server IP

 

address.

 

Leave this field blank if all domain zones are served by the specified DNS server(s).

 

 

DNS Server

Select the DNS Server(s) from ISP radio button if your ISP dynamically assigns

 

DNS server information. The fields below display the (read-only) DNS server IP

 

address(es) that the ISP assigns. N/A displays for any DNS server IP address fields

 

for which the ISP does not assign an IP address. N/A displays for all of the DNS

 

server IP address fields if the ZyWALL has a fixed WAN IP address.

 

Select Public DNS Server if you have the IP address of a DNS server. The IP

 

address must be public or a private address on your local LAN. Enter the DNS

 

server's IP address in the field to the right.

 

Public DNS Server entries with the IP address set to 0.0.0.0 are not allowed.

 

Select Private DNS Server if the DNS server has a private IP address and is located

 

behind a VPN peer. Enter the DNS server's IP address in the field to the right.

 

With a private DNS server, you must also configure the first DNS server entry for the

 

LAN, DMZ and/or WLAN in the DNS DHCP screen to use DNS Relay.

 

You must also configure a VPN rule since the ZyWALL uses a VPN tunnel when it

 

relays DNS queries to the private DNS server. The rule must include the LAN IP

 

address of the ZyWALL as a local IP address and the IP address of the DNS server

 

as a remote IP address.

 

Private DNS Server entries with the IP address set to 0.0.0.0 are not allowed.

 

 

Apply

Click Apply to save your changes back to the ZyWALL.

 

 

Cancel

Click Cancel to exit this screen without saving.

 

 

26.7 DNS Cache

DNS cache is the temporary storage area where a router stores responses from DNS servers. When the ZyWALL receives a positive or negative response for a DNS query, it records the response in the DNS cache. A positive response means that the ZyWALL received the IP address for a domain name that it checked with a DNS server within the five second DNS timeout period. A negative response means that the ZyWALL did not receive a response for a query it sent to a DNS server within the five second DNS timeout period.

When the ZyWALL receives DNS queries, it compares them against the DNS cache before querying a DNS server. If the DNS query matches a positive entry, the ZyWALL responses with the IP address from the entry. If the DNS query matches a negative entry, the ZyWALL replies that the DNS query failed.

Chapter 26 DNS

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