Wireless Access Point
HNW150AP
User Manual
140
23. 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.
Registering With Dynamic DNS Service Provider
Currently, Wireless Gateway supports two Dynamic DNS service providers, www.tzo.com and
www.dyndns.com. To use their Dynamic DNS service, you first need to visit the Web site of a service
provider and register. While registering, you need to provide your username, password, and hostname as
mandatory parameters. A service provider may also prompt you to fill some optional parameters.
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