How to configure DNS If I use the plugin yet-another-multi-site-manager?

You will have to get a dedicated IP to make things simpler.

It works exactly like the domain mapping plugin, with the exception that you need to create a wildcard A record.

Unlike domain mapping, you can’t get around the dedicated IP requirement by parking the domain, as parking will only cover the main 3.domain.com, and not any non existing *.3.mydomain.com subdomains. cPanel does not seem to support this via their admin interface. It is however possible to manually edit your apache conf file and add them to the ServerAlias line in your virtualhost: ServerAlias 3.domain.com *.3.domain.com