Frequently Asked Questions

What does Posadis mean?

Posadis is named after a (randomally picked) city somewhere in South America, called “Posadas”. To prevent ambiguity, I changed one character of the name. “Las Posadas” is the name of the week before Christmas in Mexico.

Who's behind this?

The Posadis project was founded on 31 April 2001 by Meilof Veeningen. Jama Poulsen has made some contributions to the project, though he is no longer active in the development. Sebastian Weber used to maintain a German translation of at

Is Posadis stable enough for production uses?

We believe that the latest Posadis can be considered reasonably stable. Though it isn’t as time-tested as some other nameservers, we believe it works quite well. Obviously, running Posadis is entirely at your own responsibility, as it is covered by the GNU General Public License.

How can I use DNS to maintain different domain names on one server?

All DNS is designed for, is to map IP numbers to domain names. As far as DNS is concerned, you can map multiple domain names to the same IP number. It is up to the web server running on that IP number to distinguish requests for different domain names.

This feature, often referred to as virtual hosting, is supported by most modern webservers. For example, if you’re running Apache, you can find documentation on how to do virtual hosting at this page (for Apache 2.0), or here (for Apache 1.3). A Microsoft Knowledge Base article on virtual hosting in IIS can be found here.

How can I use DNS to connect to a nonstandard port for a service?

AKA: Is there a way to specify the port for a web server not using port 80 in Posadis DNS? That is, if is on IP address x.x.x.x but using port 2000 instead of 80, can Posadis enable users to simply use rather than to access the site?

The hard truth is that this is not possible with DNS. The only thing DNS is designed for is to map domain names to IP numbers, not ports. That’s the short answer; however, I have a longer answer as well.

First, there does actually exist a method to specify a port for a service, by means of the SRV resource record type, but unfortunately, support for this method is very thin. Windows 2000 has some support for it, but other operating systems just don’t tend to bother looking up SRV record. This really a pity given how useful these could be.

Apart from that, there aren’t really that much uses for running servers on a nonstandard port. If you want to host multiple domains on one host, the way to do that is by using a web server feature called “virtual hosting” (see the previous question for more details). If on the other hand your ISP doesn’t let you run a HTTP server on a nonstandard port, you’re pretty much out of luck as far as DNS is concerned. You could let someone else host your domain and put a redirect page to your server, but apart from that there aren’t much other possibilities.

Can I use DNS to direct different domains to different local network PC's?

You cannot use DNS to direct clients from the internet to different local network PC’s depending on the domain name used (you can, off course, use DNS internally in your network to give PC’s domain names). The way DNS works is that when the client wants to connect to a domain name, at first it asks for the IP number attached to that domain name, and when it gets that IP number, it connects to that. So that IP number would have to be the public internet IP number (not the local net IP), otherwise the clients would not be able to connect.

What you’d want to do probably is just do port forwarding at the internet-visible PC to make sure different services get to different PC’s. Standalone routers usually provide that kind of service, and I bet there are tons of pieces of software for your PC to do that as well. If you’d want different domain names forwarded to different local net PC’s, you might succeed in doing something with the name-based virtual hosting option of your web server, though I’m not quite sure how that would work.

See this forum topic for more information, particularly the last post with instructions on setting up the Xitami web server to do this.

Posadis gives me a message 'Could not bind to socket'. What's wrong?

If you’re running Microsoft Internet Connection Sharing, that can cause problems with Posadis because it has its own DNS server. The ICS server listens to the UDP and TCP ports 53 of your local network interface. If you want to run Posadis on a machine running ICS, you can make it listen to your internet connection only by using the Listen configuration setting.

If you run Posadis on a Unix box, check whether you have sufficient permissions to run a DNS server. You need to be root to be able to listen to port 53, the port DNS uses.

If the address in the error message is an IPv6 address, you should check whether your operating system has IPv6 support. For Windows 2000 and XP, you need to perform additional steps to get IPv6 running; refer to the Posadis manual for details.

Posadis crashes on my (RedHat) Linux box. What's wrong?

The thread libraries shipped with RedHat 9 contain an error causing Posadis not to work. The solution is to upgrade your thread libraries. Instructions on how to do that can be found here. I don’t know whether other distributions also ship this thread library, but if so, check for updates in glibc and check whether that solves your problem.

Of course, the cause may also be something completely different, and even a bug in Posadis itself! If you experience Posadis crashing, be sure to contact me at so that I can solve the problem.

I have a question not covered in this FAQ. What should I do?

  posadis/faq.txt · Last modified: 2005/04/28 15:30
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