D-Link DFL-260 Product Manual - Page 140
Note: A high rate of server queries can cause problems, Dynamic DNS
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3.9. DNS Chapter 3. Fundamentals 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. 140