AIR Wiki: Installation of mDNSResponder

Installation of mDNSResponder

Contents of mDNSResponder

mDNSResponder takes care of two basic things:

multicast DNS, for resolving of hostnames
DNS-SD for Service Discovery using DNS

It will not take care of link-local IP addresses. For that, please use ZCIP∞ or zeroconf∞.

Alternative implementations of mDNS (and DNS-SD) include tmdns∞, howl∞, Avahi∞, Liaison∞ and pyZeroConf∞.

Download

First of all, download mDNSResponder. Depending on your OS:

For Mac OS X, it is already available in the OS. No need to install anything.
For Windows, go to http://www.apple.com/support/downloads/bonjourforwindows_readme.html∞. Optionally, you can also download the Bonjour SDK at http://developer.apple.com/networking/bonjour/download/∞
For Linux, get the source code at http://developer.apple.com/darwin/projects/bonjour/∞ and compile it yourself. Alternatively, you can follow the link to the CVS version on that page.

Installation

tar xzf
cd mDNSResponder-58.8/mDNSPosix
make os=linux
make install os=linux

Note that the mDNSResponder installer in mDNSPosix only installs the daemon (along with init.d script and libnss_mdns), but not user-level applications, like mDNSResponderClient and mDNSIdentify.

Testing

On vangogh8:

build/mDNSResponderPosix -n vangogh8

On vangogh7:

build/mDNSIdentify vangogh8.local

Result:

vangogh8.local. Addr 195.169.124.42
vangogh8.local. Addr 169.254.131.94
Host has no HINFO record; Best guess is Jaguar version of mDNSResponder with no IPv6 support

Enable Bonjour in Applications

Bonjour contains a multicast DNS server, which listens on (multicast) IP address 224.0.0.251 (as well as on FF02::FB), port 5353. Now, if your application wants to make specific use of DNS service discovery (DNS-SD), you just hook up to the API found in /usr/include/dns-sd.h. However, if you don't care about service discovery, but only in name resolution, you will not use that API, but instead just want to use gethostbyaddr() and gethostbyname(). In fact, you probably want that all existing applications which already use these two functions in the socket library are not changed, but fully automatically can map from mycomputer.local. to 169.254.13.68 and back.

There are two ways to modify the behaviour of gethostbyaddr() and gethostbyname to do just that:

Add mDNS to the Name Service Switch
Install a DNS server at localhost, and forward mDNS queries to port 5353

Add mDNS to the Name Service Switch

NSS_MDNS (mDNS for Name Service Switch) library

A great thing about mDNSResponder is, that it not only installs the mdns daemon (called mdnsd rather then mDNSResponder on linux), but also a library called libnss_mdns, which takes care that the appropriate lookups by gethostbyname() and gethostbyaddr() are handled by mdns, rather then by dns. It does so, by modifying /etc/nsswitch.conf to list "hosts: files mdns dns" instead of "hosts: files dns".

Install a DNS server at localhost, and forward mDNS queries to port 5353

(to be written)

AIR Wiki : mDNSResponderInstallation