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- .TH "SYNCTHING-LOCALDISCO" "7" "Sep 14, 2022" "v1.21.0" "Syncthing"
- .SH NAME
- syncthing-localdisco \- Local Discovery Protocol v4
- .SH MODE OF OPERATION
- .sp
- Each participating device periodically sends an Announcement packet. It also
- keeps a table of the announcements it has seen. There is no way to solicit a
- reply; the only message type is Announcement.
- .sp
- On multihomed hosts the announcement packets should be sent on each interface
- on which Syncthing will accept connections.
- .sp
- The announcement packet is sent over UDP.
- .sp
- For IPv4, the Announcement packet is broadcast either to the link\-specific
- broadcast address, or to the generic link\-local broadcast address
- \fB255.255.255.255\fP, with destination port 21027.
- .sp
- For IPv6, the Announcement packet is multicast to the transient link\-local
- multicast address \fBff12::8384\fP, with destination port 21027.
- .sp
- It is recommended that local discovery Announcement packets be sent on a 30
- to 60 second interval, possibly with immediate transmissions when a
- previously unknown device is discovered or a device has restarted (see the
- \fBinstance_id\fP field).
- .SH DEVICE ID
- .sp
- The device ID is the SHA\-256 (32 bytes) of the device X.509 certificate. See
- device\-ids in the Syncthing documentation.
- .SH ANNOUNCEMENT PACKET
- .sp
- The Announcement packet has the following structure:
- .INDENT 0.0
- .INDENT 3.5
- .sp
- .nf
- .ft C
- 0 1 2 3
- 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
- +\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+
- | Magic |
- +\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+
- / /
- \e Announce Message \e
- / /
- +\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+
- .ft P
- .fi
- .UNINDENT
- .UNINDENT
- .sp
- There is no explicit length field as the length is given by the length of
- the discovery announcement packet itself.
- .sp
- The Magic field is a 32 bit word representing 0x2EA7D90B in network (big
- endian) byte order. It identifies the packet as being a Syncthing discovery
- protocol packet.
- .sp
- The Announce Message contents are in protocol buffer format using the
- following schema:
- .INDENT 0.0
- .INDENT 3.5
- .sp
- .nf
- .ft C
- message Announce {
- bytes id = 1;
- repeated string addresses = 2;
- int64 instance_id = 3;
- }
- .ft P
- .fi
- .UNINDENT
- .UNINDENT
- .sp
- The \fBid\fP field contains the Device ID of the sending device.
- .sp
- The \fBaddresses\fP field contains a list of addresses where the device can be
- contacted. Direct connections will typically have the \fBtcp://\fP scheme.
- Relay connections will typically use the \fBrelay://\fP scheme.
- .sp
- When interpreting addresses with an unspecified address, e.g.,
- \fBtcp://0.0.0.0:22000\fP or \fBtcp://:42424\fP, the source address of the
- discovery announcement is to be used.
- .sp
- The \fBinstance_id\fP field is set to a randomly generated ID at client
- startup. Other devices on the network can detect a change in instance ID
- between two announces and conclude that the announcing device has restarted.
- .SH AUTHOR
- The Syncthing Authors
- .SH COPYRIGHT
- 2014-2019, The Syncthing Authors
- .\" Generated by docutils manpage writer.
- .
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