Dynamic DNS
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 IP address that can
change.
Dynamic DNS can also be useful in 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 NetDefendOS VPN keep
alive feature solves this problem.
Under System > Misc. Clients in the WebUI, several dynamic DNS services are defined. The
HTTP Poster client is a generic dynamic DNS client with which it is possible to define 3 different
DNS URLs plus an explicit value for Delay in seconds until all URLs are refetched (with a default
of 604800 seconds, equivalent to 7 days).
At the end of each time interval HTTP Poster will send an HTTP GET request to the defined URLs.
When NetDefendOS is reconfigured a request is NOT automatically sent. However, there is one
exception to this and that is after a reconfigure which is the result of getting a new local IP address
on the interface that connects to the DNS server.
The difference between HTTP Poster and the named DNS servers in the WebUI is that HTTP Poster
can be used to send any URL. The named services are a convenience that make it easy to correctly
format the URL needed for that service. For example, the http:// URL for the dyndns.org service
might be:
myuid:[email protected]/nic/update?hostname=mydns.dyndns.org
This could be sent as shown above by using HTTP Poster, or the URL could be automatically
formatted for the administrator by NetDefendOS through choosing the DynDNS menu option and
entering the information required for dyndns.org.
The CLI console command httpposter can be used to troubleshoot problems by seeing what
NetDefendOS is sending and what the servers are returning.
Note: A high rate of server queries can cause problems
Dynamic DNS services are often sensitive to repeated logon attempt over short periods
of time and may blacklist IP addresses that are sending excessive requests. It is
therefore not advisable to query these services too often otherwise they may cease to
respond.
HTTP Poster may be used for other purposes than dynamic DNS. Any need for NetDefendOS to
generate an HTTP GET request can be met by the feature.
3.9. DNS
Chapter 3. Fundamentals
145
Summary of Contents for DFL-1600 - Security Appliance
Page 27: ...1 3 NetDefendOS State Engine Packet Flow Chapter 1 NetDefendOS Overview 27 ...
Page 79: ...2 7 3 Restore to Factory Defaults Chapter 2 Management and Maintenance 79 ...
Page 146: ...3 9 DNS Chapter 3 Fundamentals 146 ...
Page 227: ...4 7 5 Advanced Settings for Transparent Mode Chapter 4 Routing 227 ...
Page 241: ...5 4 IP Pools Chapter 5 DHCP Services 241 ...
Page 339: ...6 7 Blacklisting Hosts and Networks Chapter 6 Security Mechanisms 339 ...
Page 360: ...7 4 7 SAT and FwdFast Rules Chapter 7 Address Translation 360 ...
Page 382: ...8 3 Customizing HTML Pages Chapter 8 User Authentication 382 ...
Page 386: ... The TLS ALG 9 1 5 The TLS Alternative for VPN Chapter 9 VPN 386 ...
Page 439: ...Figure 9 3 PPTP Client Usage 9 5 4 PPTP L2TP Clients Chapter 9 VPN 439 ...
Page 450: ...9 7 6 Specific Symptoms Chapter 9 VPN 450 ...
Page 488: ...10 4 6 Setting Up SLB_SAT Rules Chapter 10 Traffic Management 488 ...
Page 503: ...11 6 HA Advanced Settings Chapter 11 High Availability 503 ...
Page 510: ...12 3 5 Limitations Chapter 12 ZoneDefense 510 ...
Page 533: ...13 9 Miscellaneous Settings Chapter 13 Advanced Settings 533 ...