mDNS Multicast Network Traffic Filter

Why can't I see shared devices on the network?


The Office of Information Technology Services filters mDNS (Multicast Domain Name Service) traffic on the campus network. We have found that mDNS degrades the performance of the campus network and is not necessary for the services supported.

What is mDNS?

mDNS (Multicast Domain Name Service) is a name service feature created primarily for small home networks and small office networks. This service allows network devices to connect through the use of common names “Suzie’s Computer”. This is done through broadcast advertising of the name system and the shared resources like printers and files. OC’s enterprise network supports DNS (Domain Name Service) which differs from mDNS in that it is a unicast service as opposed to a multicast or broadcast service.

Why is IT Services Filtering mDNS traffic?

mDNS was not designed for use on large networks. mDNS generates large amounts of network traffic that has had a significant impact on the performance of the campus network.

What does all this mean to me?

In short you will no longer see services that rely on mDNS. This may include:

  • The inability to share iTunes music between network attached computers.
  • Applications using Bonjour (Apple’s IETF ZEROCONF suite of communication protocols) will no longer work across the campus network.
  • If using iChat you must use an AIM (AOL Instant Messaging), .Mac or Jabber account rather than Bonjour.
  • Some iPhone/iPod applications that depend on mDNS services will no longer function, such as Remote, Rowmote, and others.
  • Personal printers purchased for use in campus housing may need to be reconfigured or connected via cable.
  • The inability to “browse” and locate printers and files servers on the campus network. You will be required to specify the network share name as most do currently.

The filtering and/or blocking of mDNS does not indicate that IT Services disapproves of the service and at this point we do not require that this service be disabled on network devices. IT Services has only taken this action to limit the ability of mDNS to adversely affect network performance.

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