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From: Doug Hardie <bc979@lafn.org>
Subject: Re: kern/172683: [ip6] Duplicate IPv6 Link Local Addresses
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The following reply was made to PR kern/172683; it has been noted by GNATS.

From: Doug Hardie <bc979@lafn.org>
To: bug-followup@FreeBSD.org
Cc:  
Subject: Re: kern/172683: [ip6] Duplicate IPv6 Link Local Addresses
Date: Sun, 14 Oct 2012 16:42:50 -0700

 Here is some more interesting information on the issue.  RFC 4862 states =
 that if the link-local address is MAC based then it should bring down =
 the link and log the duplicate address error.  Kurt Jaeger pointed out =
 in a private email that there is a sysctl that is supposed to control =
 this behavior: net.inet6.ip6.dad_count.  The value 1 is to permit the =
 interface to continue to operate and the value 2 is to stop operation.  =
 Sure enough net.inet6.ip6.dad_count =3D 1 as the default value.  I =
 changed it to 2 and ran the tests again.  There was no change in the =
 performance.  The interface remained in use and nothing was logged in =
 /var/log/messages.  Unfortunately I no longer have a Vista machine to =
 test with since it generates non-MAC related link-local addresses.  XP =
 and Win 7 both use MAC based addresses.  Using Vista talking to FreeBSD =
 7.2, the Neighbor Advertisement was returned by FreeBSD and Vista chose =
 another link-local address.=