What Is the mDNS Protocol?

mDNS is an address lookup system for small networks.

DNS is the Domain Name Service. This provides translation between a web address (starting with "www") and IP (Internet Protocol) addresses. mDNS is the Multicast DNS protocol. A "multicast" forwards the same message to many endpoints on a network. mDNS is a method of network neighborhood discovery.

Function

Where a network does not have access to the DNS system, either by policy or by absence of infrastructure (as in Mobile Ad Hoc Networks), mDNS enables local lookup tables to be compiled. Each device attached to an mDNS-enabled network sends out a message detailing its name, function and capabilities. Each receiving device stores this information so it can route requests when an application requests a service, such as printing.

Features

The protocol is better suited to small networks. Its method of notification can cause a lot of traffic to build up on larger networks connecting many devices. Messages are sent out at regular intervals and cause excess unwanted traffic on the network.

Future

mDNS is particularly useful in the developing field of wireless networks. WiFi laptops are able to communicate directly with each other without resorting to any infrastructure such as routers or Internet service providers. In these environments mDNS enables neighboring computers to quickly compile a map of interconnecting nodes, creating an ad hoc network.

References

• Office of Information Technology, Princeton University: "OIT Filters mDNS (Multicast Domain Name Service)"
• Internet Engineering Task Force: Internet Draft: "Multicast DNS"