Monday, April 09, 2007

Bringing the ease of AppleTalk to wide area IP

Nice review by ars technica ...
Have your Mac say Bonjour to tout le monde

By now, most Mac users are probably familiar with the magic that is Bonjour (formerly known as Rendezvous). A decade or two ago, when local networks emerged, many computer vendors came up with their own network protocols—AppleTalk in Apple's case. Unlike TCP/IP, AppleTalk works completely automatically: addresses are selected without user intervention or even a DHCP server, and the network makes sure all hosts know about all the network services that are available. Since the demise of the vendor-specific network protocols, Apple has been working hard to add the same level of seamlessness and ease-of-use to today's IP networks. On local networks, this has worked very well for a number of years: you can automatically detect other people running iChat, iTunes, and iPhoto, as well as detect local file, print, and web servers. All of this works by virtue of multicast DNS, where all the systems on a local network listen for mDNS requests and reply if they can answer the request. Unfortunately, this mechanism can't work across the Internet: before long, the only traffic we'd see would be mDNS requests.

It turns out that the Bonjour that we all know and love has a little-known sibling that does work across the Internet: Wide-Area Bonjour. And it's part of Mac OS X Tiger. It works like this. When you get an IP address from your friendly neighborhood DHCP server, the DHCP server usually also supplies a domain name. Wide-Area Bonjour looks up a couple of special DNS names under the supplied domain name. In most cases, these lookups fail and nothing
My oddball Brother MFC has Bonjour (mDNS) support. I recommend not buying any networkable device that lacks support for mDNS, though it's very hard to learn which devices do this. (Heck, most product descriptions don't even identify which devices have Ethernet ports!)

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