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124 lines
4.1 KiB
Groff
124 lines
4.1 KiB
Groff
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..
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.TH "SYNCTHING-LOCALDISCO" "7" "Jan 31, 2022" "v1" "Syncthing"
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.SH NAME
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syncthing-localdisco \- Local Discovery Protocol v4
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.SH MODE OF OPERATION
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.sp
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Each participating device periodically sends an Announcement packet. It also
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keeps a table of the announcements it has seen. There is no way to solicit a
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reply; the only message type is Announcement.
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.sp
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On multihomed hosts the announcement packets should be sent on each interface
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on which Syncthing will accept connections.
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.sp
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The announcement packet is sent over UDP.
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.sp
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For IPv4, the Announcement packet is broadcast either to the link\-specific
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broadcast address, or to the generic link\-local broadcast address
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\fB255.255.255.255\fP, with destination port 21027.
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.sp
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For IPv6, the Announcement packet is multicast to the transient link\-local
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multicast address \fBff12::8384\fP, with destination port 21027.
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.sp
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It is recommended that local discovery Announcement packets be sent on a 30
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to 60 second interval, possibly with immediate transmissions when a
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previously unknown device is discovered or a device has restarted (see the
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\fBinstance_id\fP field).
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.SH DEVICE ID
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.sp
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The device ID is the SHA\-256 (32 bytes) of the device X.509 certificate. See
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device\-ids in the Syncthing documentation.
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.SH ANNOUNCEMENT PACKET
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.sp
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The Announcement packet has the following structure:
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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0 1 2 3
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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
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+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+
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| Magic |
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+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+
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/ /
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\e Announce Message \e
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/ /
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+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+\-+
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.sp
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There is no explicit length field as the length is given by the length of
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the discovery announcement packet itself.
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.sp
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The Magic field is a 32 bit word representing 0x2EA7D90B in network (big
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endian) byte order. It identifies the packet as being a Syncthing discovery
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protocol packet.
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.sp
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The Announce Message contents are in protocol buffer format using the
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following schema:
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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message Announce {
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bytes id = 1;
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repeated string addresses = 2;
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int64 instance_id = 3;
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}
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.sp
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The \fBid\fP field contains the Device ID of the sending device.
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.sp
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The \fBaddresses\fP field contains a list of addresses where the device can be
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contacted. Direct connections will typically have the \fBtcp://\fP scheme.
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Relay connections will typically use the \fBrelay://\fP scheme.
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.sp
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When interpreting addresses with an unspecified address, e.g.,
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\fBtcp://0.0.0.0:22000\fP or \fBtcp://:42424\fP, the source address of the
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discovery announcement is to be used.
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.sp
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The \fBinstance_id\fP field is set to a randomly generated ID at client
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startup. Other devices on the network can detect a change in instance ID
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between two announces and conclude that the announcing device has restarted.
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.SH AUTHOR
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The Syncthing Authors
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.SH COPYRIGHT
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2014-2019, The Syncthing Authors
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.\" Generated by docutils manpage writer.
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