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doc: improve FAQ

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Miroslav Lichvar 2018-03-27 17:57:17 +02:00
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doc/faq.adoc
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@ -393,16 +393,31 @@ things
Some other program running on the system may be using the device.
=== What if my computer does not have an RTC or backup battery?
In this case you can still use the `-s` option to set the system clock to the
last modification time of the drift file, which should correspond to the system
time when `chronyd` was previously stopped. The initial system time will be
increasing across reboots and applications started after `chronyd` will not
observe backward steps.
== NTP-specific issues
=== Can `chronyd` be driven from broadcast NTP servers?
=== Can `chronyd` be driven from broadcast/multicast NTP servers?
No, the broadcast client mode is not supported and there is currently no plan
to implement it. The broadcast and multicast modes are inherently less
accurate and less secure (even with authentication) than the ordinary
server/client mode and they are not as useful as they used to be. Even with
very modest hardware a single NTP server can serve time to hundreds of
thousands of clients using the ordinary mode.
No, the broadcast/multicast client mode is not supported and there is currently
no plan to implement it. While the mode may be useful to simplify configuration
of clients in large networks, it is inherently less accurate and less secure
(even with authentication) than the ordinary client/server mode.
When configuring a large number of clients in a network, it is recommended to
use the `pool` directive with a DNS name which resolves to addresses of
multiple NTP servers. The clients will automatically replace the servers when
they become unreachable, or otherwise unsuitable for synchronisation, with new
servers from the pool.
Even with very modest hardware, an NTP server can serve time to hundreds of
thousands of clients using the ordinary client/server mode.
=== Can `chronyd` transmit broadcast NTP packets?