Apple Bonjour is a LAN protocol similar to Microsoft suite of protocols for querying Local Area Network resources: Bonjour (mDNSResponder), AirPlay, Home Sharing, Printer Discovery, etc. On Macintosh this service is provided by the mDNSResponder over IP and IPv6.

This is a multicast protocol. Each node listens for broadcasts over the LAN to the multicast address, 224.0.0.251/24 network for queries. And respond with a list of services that they have to offer using the same multicast address. Normally, this traffic should not leave the broadcast domain, LAN-to-LAN only.

This SonicWALL signature identifies Apple Bonjour Protocol over UDP/5353..