D-Link NetDefendOS User Manual page 282

• Primary Server: 10.0.0.1
• Secondary Server: 10.0.0.2
3. Click OK
Automatic DNS Address Assignment
DNS addresses can also be assigned by enabling DHCP (for IPv6) or DHCPv6 (for IPv6 addresses)
for any interface that is connected to an external DHCP server. This is often used when accessing
the Internet via an ISP and receiving all the required addresses from the ISP's DHCP server.
The DNS addresses that are received through DHCP on any interface will become the system
wide NetDefendOS DNS servers if no static DNS addresses have already been configured.
However, if static DNS addresses have been manually configured then any DNS server addresses
received via DHCP on any interface will be ignored and the existing manually configured DNS
addresses will not be affected.
Using DHCP for configuring DNS addresses is discussed further in Section 5.2, "IPv4 DHCP Client"
and Section 5.6.1, "DHCPv6 Client".
DNS Lookup and IP Rules
In the case of DNS server request being generated by NetDefendOS itself, no IP rules need to be
defined for the connection to succeed. This is because connections initiated by NetDefendOS are
considered to be trusted. For example, this would be the case if NetDefendOS is accessing a CA
server to establish the validity of a certificate and first needs to resolve the certificate's FQDN to
an IP address.
Dynamic DNS and HTTP Poster
A DNS feature offered by NetDefendOS is the ability to explicitly inform DNS servers when the
external IP address of the NetDefend Firewall has changed. This is sometimes referred to as
Dynamic DNS and is useful where the NetDefend Firewall has an external address that can
change.
Dynamic DNS can also be useful in IPsec VPN scenarios where both ends of the tunnel have
dynamic IP addresses. If only one side of the tunnel has a dynamic address then the Auto
Establish property of the IPsec Tunnel object can solve this problem.
Under Network > Network Services in the Web Interface, several dynamic DNS services are
defined. The HTTP Poster client object is a generic dynamic DNS client with the following
characteristics:
• Multiple HTTP Poster objects can be defined, each with a different URL and different optional
settings.
• By default, an HTTP Poster object sends an HTTP GET request to the defined URL. Some servers
require an HTTP POST request and to achieve this the option HTTP Post the Values should be
enabled. This is usually needed when authentication parameters are being sent in the URL.
• By default, HTTP Poster does not automatically send the server request after NetDefendOS
reconfiguration. This behavior can be changed by enabling the option Repost on each
reconfiguration.
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Chapter 3: Fundamentals