Dynamic DNS Update Client

Name

DYNDNS -- Dynamic DNS Update Client.

Description

More and more people these days have dynamic IP addresses, i.e. IP addresses which are assigned by their Internet Service Provider and which may be different each time they log on. Broadband users are permanently connected to the internet, but even their IP addresses may be changed at any time by the ISP, unless they pay extra for a static address.

For the normal internet user this is not a problem, because no-one else needs to know their IP address. However, if you want other people to be able to connect to your system, e.g. if you are running a web server, they need to know your current IP address. This is where the dynamic DNS providers come in.

There are many organisations providing dynamic DNS services, such as dyndns.org, noip.com, duckdns.org etc. It is easy, and often free, to set up an account with one of these providers, and after doing so you may choose one or more hostnames for your system, for example "g8pzt.ath.cx".

All you then have to do is keep the dns provider informed of your current IP address, either manually or using an automatic update client. Whenever someone asks their system to connect to "g8pzt.ath.cx", they are given its current IP address.

XRPi has an integral client for automatically maintaining dynamic DNS entries, thus obviating the need to run an external client or perform manual updates. If the client is enabled, and your IP address changes, the client will update one or more hostname entries on the DNS server. If you do not use dynamic dns, you need read no further.

The client is enabled by including the directive DYNDNS=1 in the relevant PORT configuration block in XROUTER.CFG, i.e. the port which is connected to the Internet. DYNDNS=0 disables the client, as does omitting the directive altogether. Note: you must only use this directive on ONE port, and you may crash XRPi if you try to use it on more than one.

The client requires a configuration file, DYNDNS.CFG, and it creates a data file DYNDNS.BIN. The configuration file is heavily commented, so it should be self-explanatory.

If your XRPi is *directly* connected to the Internet, i.e. via a PSTN modem or non-routing cable modem, the client simply monitors the port IP address (which is assigned by the ISP using IPCP or DHCP), and informs the dynamic dns server if it changes. This mode is selected by putting "NO" on the "Use external IP detection service" configuration line in DYNDNS.CFG.

However, if your connection to the Internet is via a NAT router such as an ADSL modem/router or Windows ICS, the port IP address will be a "private" one which no-one else could access. In this case, the client can be configured to query an external IP address detection service at regular intervals, updating the DNS server if a change is detected. This mode is selected by putting "YES" on the "Use external IP detection service" configuration line.

Free accounts on dynamic DNS providers are usually removed if they haven't been updated for 35 days. Thus, if your IP address hasn't changed for 30 days, the client automatically sends an update to keep the account refreshed.

You may have more than one hostname associated with your IP address, but that's not a problem. In the "hostname(s) to be updated" line, simply list the hostname, separated by commas. Be careful not to include any spaces or mistakes in the line.

Nowadays, most domestic routers include dynamic dns update clients, so in most cases XRPi's client would not be needed.

Files

DYNDNS.CFG(8) -- Dyndns Client Configuration file.
XROUTER.CFG(8) -- XRPi Configuration File.

Caveats

This client was written for XR16 at the turn of the century, when dyndns.org offered free accounts, which they no longer do.

Although there are other free providers, their update rules may be different. For example, noip.com will remove free accounts unless you log in to their website via a Captcha challenge at least once every 30 days. The automatic update alone is not sufficient to keep the account alive.

Dynamic DNS providers have strict rules governing how often a client may send updates with an unchanged IP address. If you send updates for unchanged addresses more frequently than (typically) 30 days, it is considered to be abuse, and your client will be locked out. So don't delete DYNDNS.BIN, which keeps track of when you last updated.