c2691d8e7c
RFC 5227 specifies randomized intervals to avoid that a large number of hosts
powered up at the same time send their message simultaneously. Performing the
conflict detection takes a variable time between 4 and 7 seconds from the
beginning to the first announcement, as shown by the following diagram where P
indicates a probe and A an announcement:
time(s) 0 1 2 3 4 5 6 7 8 9
+---+---+---+---+---+---+---+---+---+
SHORTEST P P P A A
LONGEST P P P A A
The host can't use the address until the first announcement is sent. 7 seconds
is a very long time on modern computers especially considering the fact that
the round-trip time on current LAN technologies is at most few milliseconds.
Section 2.2 of the RFC addresses this matter and hints that a future standard
will adjust those timeouts; however that standard doesn't exist yet.
Make the timeout configurable via a new IPv4DuplicateAddressDetectionTimeoutSec=
option. The intervals defined in the RFC are then scaled proportionally so that
the duration of the conflict detection takes at most the given value. Interval
happening after the first announcement are not scaled, as recommended by the
RFC.
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