Standards/Ethernet/Bonjour
(→Host discovery) |
(→Multicast frames) |
||
| Line 18: | Line 18: | ||
Bonjour frames are filtered in [http://www.wireshark.org/ Wireshark] with the help of the expression: | Bonjour frames are filtered in [http://www.wireshark.org/ Wireshark] with the help of the expression: | ||
ip.version==4 and udp.port==5353 | ip.version==4 and udp.port==5353 | ||
| + | |||
| + | The frame structure is based on the [http://www.netfor2.com/dns.htm DNS packet format]. | ||
| + | It is built out of 2 parts: header and data. | ||
| + | |||
| + | {| class="wikitable" style="margin: 0 auto; text-align: center;" | ||
| + | |- style="text-align:center;" | ||
| + | ! offset (bytes) | ||
| + | ! style="width:150px;"|0 | ||
| + | ! style="width:150px;"|1 | ||
| + | |- | ||
| + | ! 0 | ||
| + | | colspan="2" | ID = 0x0000 | ||
| + | |- | ||
| + | ! 2 | ||
| + | | colspan="2" | Flags | ||
| + | |- | ||
| + | ! 4 | ||
| + | | colspan="2" | QDCOUNT | ||
| + | |- | ||
| + | ! 6 | ||
| + | | colspan="2" | ANCOUNT | ||
| + | |- | ||
| + | ! 8 | ||
| + | | colspan="2" | NSCOUNT | ||
| + | |- | ||
| + | ! 10 | ||
| + | | colspan="2" | ARCOUNT | ||
| + | |- | ||
| + | ! 12 | ||
| + | | colspan="2" style="background:#fdd;" | <br />Data<br /> | ||
| + | |} | ||
| + | |||
| + | The flags are all <code>0</code> except for: | ||
| + | * the first bit, Query/Response (QR), which is <code>0</code> for a query and <code>1</code> for 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 [http://en.wikipedia.org/wiki/List_of_DNS_record_types <code>QTYPE</code>] which is 0x0001 for a host address, and <code>QCLASS</code> which is 0x0001 for Internet. | ||
== Host discovery == | == Host discovery == | ||
Revision as of 14:40, 5 June 2012
|
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 | |
| 6 | ANCOUNT | |
| 8 | NSCOUNT | |
| 10 | ARCOUNT | |
| 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:
