IPv6 DAD

[Doug Hardie]

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.  

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.  

-- Doug