2 @unnumbered MultiCast Discovery
4 MCD is an addition to online @ref{Sync, synchronization protocol}, that
5 gives ability to make node discovery by sending multicast announcements
6 in local area network. It is very simple:
10 @command{nncp-daemon} sends multicast messages about its presence
12 See @ref{CfgMCDSend, mcd-send} configuration option.
14 When @command{nncp-caller} sees them, it adds them as the most
15 preferred addresses to already known ones. If MCD address
16 announcement was not refreshed after two minutes -- it is removed.
17 See @ref{CfgMCDListen, mcd-listen} and
18 @ref{CfgMCDIgnore, mcd-ignore} configuration options.
21 MCD announcement is an XDR-encoded packet with only two fields:
29 Magic number is @verb{|N N C P D 0x00 0x00 0x01|} and sender is 32-byte
30 identifier of the node. It is sent as UDP packet on IPv6 @verb{|ff02::1|}
31 multicast address (all hosts in the network) and hard-coded @strong{5400}
32 port. Operating system will use IPv6 link-local address as a source one,
33 with the port taken from @command{nncp-daemon}'s @option{-bind} option.
34 That way, IP packet itself will carry the link-scope reachable address