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Date:      Thu, 18 Feb 2021 18:40:51 -0800
From:      Doug Hardie <bc979@lafn.org>
To:        "net@freebsd.org" <net@FreeBSD.org>
Subject:   IPv6 DAD
Message-ID:  <1AFA2FDE-F382-4EAC-9424-E03570566125@sermon-archive.info>

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The last time I played with IPv6 (FreeBSD 9), DAD was activated when the =
network was first configured.  Once the interface came up, a neighbor =
solicitation was sent with the link-local address to see if it =
duplicated anywhere else. Trying that with FreeBSD 13.0-BETA2 it is =
quite different.  Bringing up an interface does not result in and =
solicitations.  The MAC based address is just used.  If you bring up =
another machine with that address, the neighbor solicitation is send and =
a response is received.  However, the address is still entered as shown =
in ndp.  There is no attempt to pick a different address.  However, =
ifconfig now shows duplicated:

inet6 fe80::250%bge0 prefixlen 64 duplicated scopeid 0x1

That address on the first machine to have it continues to work and is =
accessible from a third machine.

I used quite arbitrary addresses for this experiment. =20

I noticed there was a significant update to the RFCs on DAD so I suspect =
this behavior is now desired, but it is not obvious. =20

-- Doug




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