I've been using .lan, referenced in rfc6762[1] as a good alternative to the multicast .local

> We do not recommend use of unregistered top-level domains at all, but should network operators decide to do this, the following top-level domains have been used on private internal networks without the problems caused by trying to reuse ".local." for this purpose:

      .intranet.
      .internal.
      .private.
      .corp.
      .home.
      .lan.