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Enable iTunes and iPhoto sharing on newer Linksys routers
Authored by: jaaronp on May 01, '07 10:26:36AM

Just for the sake of technical accuracy: it's not the sharing that's being prevented; it's the service discovery.

These really are two distinct protocols: bonjour (formerly rendezvous) uses multicast DNS queries to discover services available on the network. This is what's being blocked by the router.

Essentially, when a service provider comes online it sends out a "hello computer X is offering serivce Y on port Z" message to everyone on your subnet (which is cached by possible consumers), and when consumers come online they (a) check their cache, and (b) send out a message like "Is anyone else offering service Y" (again to all machines on the subnet). Once the consumer has discovered the provider, it makes a direct connection to that machine. (*Note this is a very rough sketch, rendezvous does some clever caching and so forth to minimize chattiness).

The actual sharing (transfer of library data, and streaming of songs) takes place over a standard point to point TCP connection. It uses HTTP on a funny port (3689 for iTunes) as a session-layer transport, and DAAP (The Digital Audio Access Protocol), DPAP (The Digital Picture Access Protocol) to transport the library data. The songs/pictures are transmitted as raw mp3s/aacs/jpegs/whatever over the HTTP connection.

This distinction is significant because it means that if the Finder's Network Browsing isn't functional (because the switch is blocking the rendezvous mDNS traffic), you can still enter the IP address of the server in the "Connect to Server" dialog and reasonably expect to be able to establish a connection (unless the switch is also blocking the Apple Filesharing Protocol (AFP), port 548).

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