More Info on Apple's Wide Area Bonjour from Mac OS X 10.5 (Leopard)

Wide Area Bonjour is an extension to (local area) Bonjour which is Apple's zero-configuration networking protocol.

Under AppleTalk, Macs required no manual configuration to connect to a network. Macs would announce themselves, acquire a unique network address, and discover services available on the network. As Apple depreciated AppleTalk in favor of TCP/IP-based networking, they wanted a similar protocol to provide all the elegant simplicity of old AppleTalk. So, they created Bonjour, and released it as an open protocol called zeroconf.

(It was originally named Rendezvous, but they were forced to change the name by a software company in the financial space that had a technology serving a similar purpose. Obviously, they needed another French name; hence Bonjour.)

As many people know, TCP/IP (v4) requires a certain amount of configuration. Either you need a DHCP (or BOOTP) server to hand out the information to client computers, or you must manually enter it. To function, a computer needs a unique host addresses and a network address. These two addresses are combined to form an IP address. Also under most circumstances, a host will need a DNS server configured to translate domain names to IP addresses for actual use.

Bonjour uses mDNS, a multicast version of DNS, to handle domain name translations. It multicasts a request for a name-to-IP resolution, and devices configured to "listen" to that multicast address can respond. This is similar to how MAC-IP address resolution occurs, but that's another article.

The first versions of Bonjour only worked across a local area network. But with Wide Area Bonjour, the new version uses Dynamic DNS Update and regular unicast DNS queries to reach outside the local network. (this from Apple's Bonjour FAQ and RFC2136) But to do this, dedicated servers are required.

It appears to me Apple will host dynamic DNS servers (maybe via .Mac) to allow wide area functionality. The obvious possibilities are for SSH (remote shell access), SFTP (remote file transfer), and VNC (remote desktop/remote control) which will be called Back To My Mac.

But I think Apple will want to enable something a bit more flashy. I like to think they will implement things like iTunes library sharing (if the RIAA will allow it), iPhoto library sharing, and allowing developers to tie in their own services. I believe this could really make things interesting and might give Apple a real advantage vs. Windows.

Other links:
My initial post on Wide Area Bonjour
Leopard Info Sources

Leopard Feature of Interest - Wide Area Bonjour

Apple's Leopard Site

Wide Area Bonjour
Access your Macs, at home or on the road, with a single consistent host name. Use this host name whether you’re behind a NAT gateway or hopping across DHCP servers.

It sounds like this is the basis of Back to My Mac, which is a new feature in Mac OS X Leopard. It allows you to remotely access your Mac for file sharing or desktop sharing (remote control). If it works as advertised, it will be mch cleaner and easier than manualy setting up an SSH tunnel and configuring VNC and DynDNS.

Additional Bonjour links:
Apple Developer FAQ
More Detail

Leopard Info Sources