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Wi-Fi Personal Bridge 150 User Manual
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Dynamic DNS
When you want your internal server to be accessed by using DNS name rather than using the
dynamic IP address, you can use the DDNS service. The DDNS server allows to alias a dynamic IP
address to a static hostname.
This chapter provides you an overview of the Dynamic DNS feature of the modem and configuration
details related to it.
Overview
If some host has a dynamic IP address that keeps changing frequently, it is difficult to keep updating
the IP record that is associated with the domain name of this host in the zone files. This will result in
non-accessibility of this host on the Internet. Dynamic DNS service allows to keep mapping of a
dynamic IP address of such host to a static hostname. Dynamic DNS services are provided by
many websites. The host needs to register with some website and get a domain name. When the IP
address of the host changes, it just needs to send a message to the website that's providing
dynamic DNS service to this host. For this to work, an automated update client needs to be
implemented. These update clients send update messages to the servers whenever there is some
change in the IP address of that host. Then, the server updates the entries for that host and replies
back with some return code.
Above Figure explains one such scenario in which a host gets a dynamic IP address for itself from a
DHCP server. As the host has registered with one of the dynamic DNS service providers on the
Internet, it sends an update message to the service provider with host name and changed IP
address. The service provider updates the new IP address of the host in the zone files that have
entry for that host name and replies back with some return code. The return code communicates the
success or failure of the update message. This process is repeated every time the host's IP address
changes.
If the dynamic DNS service provider is notified of the same IP address again and again, then it
considers it an abuse and might block the host name. To avoid this scenario, the IP address that
was successfully updated to the ISP is stored on the unit. Whenever we receive an IP address
change notification, the new IP address is compared with the IP address that was stored on the last
update. If they differ, then only an update request is sent. However, when the system comes up
there is no way of knowing what was the IP address on last successful update before the system
went down. You need to give the command “system config save“ periodically to save this IP address
on Flash.