Standards/Ethernet/Bonjour
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| − | | colspan="2" | ANCOUNT | + | | colspan="2" | ANCOUNT (answers) |
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| − | | colspan="2" | NSCOUNT | + | | colspan="2" | NSCOUNT (authority) |
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| − | | colspan="2" | ARCOUNT | + | | colspan="2" | ARCOUNT (additional) |
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Revision as of 14:42, 5 June 2012
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Bonjour is Apple's protocol for service discovery. It is lightweight and works over UDP. Bonjour implements a Multicast Domain Name System (mDNS) service without requiring a conventional DNS server.
Bonjour comprises:
- host discovery: finding the IP addresses of
.localdevices - service discovery: listing the capabilities of the devices
Bonjour is implemented in Linux systems under the name Avahi. There is also a Windows implementation of Bonjour.
Multicast frames
The mDNS frames are sent to the multicast address 01:00:5E:00:00:FB / 224.0.0.251, from and to port 5353.
Bonjour frames are filtered in Wireshark with the help of the expression:
ip.version==4 and udp.port==5353
The frame structure is based on the DNS packet format. It is built out of 2 parts: header and data.
| offset (bytes) | 0 | 1 |
|---|---|---|
| 0 | ID = 0x0000 | |
| 2 | Flags | |
| 4 | QDCOUNT (questions) | |
| 6 | ANCOUNT (answers) | |
| 8 | NSCOUNT (authority) | |
| 10 | ARCOUNT (additional) | |
| 12 | Data | |
The flags are all 0 except for:
- the first bit, Query/Response (QR), which is
0for a query and1for a response - the sixth bit, Authoritative Answer (AR), which is equal to the bit QR
The data is the UTF-8 list of the parts of the name preceded by the length of the item.
In a question, the name is terminated with a 0x00 and followed by QTYPE which is 0x0001 for a host address, and QCLASS which is 0x0001 for Internet.
Host discovery
Query
Typing in a terminal:
ping fpga1.diploma.local
causes the computer to send the following mDNS query:
01 00 5e 00 00 fb 00 23 32 b1 21 52 08 00 45 00 00 41 e6 9d 00 00 ff 11 00 00 99 6d 05 a0 e0 00 00 fb 14 e9 14 e9 00 2d 80 47 00 00 00 00 00 01 00 00 00 00 00 00 05 66 70 67 61 31 07 64 69 70 6c 6f 6d 61 05 6c 6f 63 61 6c 00 00 01 00 01
This frame contains Ethernet header:
01 00 5e 00 00 fb 00 23 32 b1 21 52 08 00
IP header:
45 00 00 41 e6 9d 00 00 ff 11 00 00 99 6d 05 a0 e0 00 00 fb
UDP header:
14 e9 14 e9 00 2d 80 47
and mDNS payload:
00 00 00 00 00 01 00 00 00 00 00 00 05 66 70 67 61 31 07 64 69 70 6c 6f 6d 61 05 6c 6f 63 61 6c 00 00 01 00 01
Answer
To this, the selected device should respond:
