In a local network (or any other network), it’s desirable to be able to find computers by name rather than by ip address.

So, instead of using:

$ ping 192.168.178.25

one wants to use:

$ ping mycomputer

This mapping task is typically done by a DNS server.

Sometime back I wrote an article about how to ping/identify computers by name on Windows.

Unfortunately this solution highly depends on a good router that

• lets you specify names for individual ip addresses (or determines them automatically)

• provides a domain name for your local network (e.g. “fritz.box”)

Unfortunately, I recently was forced to switch to a less “superior” router that doesn’t support these features. So an alternative had to be found.

Multicast DNS ∞

Fortunately, a solution exists and this solution is called Multicast DNS (short: mDNS).

Multicast DNS lets you find computers on your local network by name. You just have to add .local to the computer’s name.

So, to ping a computer called marvin you’d use:

$ ping marvin.local

What Do I Need? ∞

There are two major mDNS implementations: Apple’s Bonjour and Microsoft’s Link-local Multicast Name Resolution (LLMNR).

Bonjour seems to have a wider adoption so I’m concentrating on this.

Here’s what you need:

• Windows: If you have iTunes installed, you’re ready to go. If you don’t want to install iTunes, you’ll need to install the Bonjour Print Services for Windows. (Don’t be bothered by the “printing” part in the name. The package is a fully functional mDNS solution and it’s the only standalone Bonjour package available for Windows anyway.)
• Linux: You need Avahi which is compatible with Bonjour. On Ubuntu/Debian, you need two packages: avahi-daemon (to be visible on the network) and libnss-mdns (to be able to find other computers)

• OS X: Everything is pre-installed. You don’t need anything else.

Notes:

• The domain .local has officially been reserved for resolving names in a local network. This means that:

  • there will never be a “real” domain ending called “.local”. So you don’t run the risk of name conflicts with the internet.
  • good routers won’t ask your ISP’s DNS server for “.local” names. So connecting to a “.local” name, will always result in an ip address from the local network.
• mDNS, of course, only works if no two computers on the local network share the same name.

• With mDNS, you don’t need to specify .local as “primary DNS suffix” on Windows – unlike the solution in the aforementioned article.