CalDAV/CardDAV discovery

If you use iCal/Calendar on Mac OS X or iOS, you might have seen that you don't have to specify the type of server ("Automatic" is the default type). But to work, you need to setup DNS entries so that iCal/Calendar can find the server for the user, and your CalDAV server must support "well-known" URLs. "well-known" is supported by iCal Server (OS X Server 10.7 or 10.8), Calendar Server (the open source version of iCal Server) and Kerio Connect (starting with version 7.5 I believe).

For DNS, I found how to do it in this article. In short, you need at least one SRV entry that will tell where your server is located. If your domain is "macti.lan", you need to add the following entry:

_caldavs._tcp.macti.lan.            10800 IN SRV      10 1 8443 server.macti.lan.

Where 8443 is the port on which your CalDAV server is running (8443 is the HTTPS port for iCal Server/Calendar Server, for Kerio Connect by default it's on port 443). server.macti.lan is the DNS name of the host running the CalDAV service.

You will notice that the DNS entry is _caldavs_. If your CalDAV server is running on a non-protected port, or if it's available on both ports, you should add a DNS entry like this:

_caldav._tcp.macti.lan.            10800 IN SRV      10 1 8008 server.macti.lan.

Notice that the 's' is missing in the DNS entry. If you have both entries, iCal/Calendar will try the secure entry first, and it's not working, it will try the non-secure entry after.

If you have a iCloud account with a @me.com, a SRV entry do exist:

$ dig _caldavs._tcp.me.com srv 
_caldavs._tcp.me.com. 3600 IN SRV 0 0 443 caldav.icloud.com.