Fix several logic bugs in the previous IPv6 variable change and

re-add $ipv6_enable support for backward compatibility.  From
UPDATING:

 1. To use IPv6, simply define $ifconfig_IF_ipv6 like $ifconfig_IF
    for IPv4.  For aliases, $ifconfig_IF_aliasN should be used.
    Note that both variables need the "inet6" keyword at the head.

    Do not set $ipv6_network_interfaces manually if you do not
    understand what you are doing.  It is not needed in most cases.

    $ipv6_ifconfig_IF and $ipv6_ifconfig_IF_aliasN still work, but
    they are obsolete.

 2. $ipv6_enable is obsolete.  Use $ipv6_prefer and/or
    "inet6 accept_rtadv" keyword in ifconfig(8) instead.

    If you define $ipv6_enable=YES, it means $ipv6_prefer=YES and
    all configured interfaces have "inet6 accept_rtadv" in the
    $ifconfig_IF_ipv6.  These are for backward compatibility.

 3. A new variable $ipv6_prefer has been added.  If NO, IPv6
    functionality of interfaces with no corresponding
    $ifconfig_IF_ipv6 is disabled by using "inet6 ifdisabled" flag,
    and the default address selection policy of ip6addrctl(8)
    is the IPv4-preferred one (see rc.d/ip6addrctl for more details).
    Note that if you want to configure IPv6 functionality on the
    disabled interfaces after boot, first you need to clear the flag by
    using ifconfig(8) like:

         ifconfig em0 inet6 -ifdisabled

    If YES, the default address selection policy is set as
    IPv6-preferred.

    The default value of $ipv6_prefer is NO.

 4. If your system need to receive Router Advertisement messages,
    define "inet6 accept_rtadv" in $ifconfig_IF_ipv6.  The rc(8)
    scripts automatically invoke rtsol(8) when the interface becomes
    UP.  The Router Advertisement messages are used for SLAAC
    (State-Less Address AutoConfiguration).

1 files changed, 9 insertions, 3 deletions

diff --git a/sbin/ifconfig/ifconfig.8 b/sbin/ifconfig/ifconfig.8
index de241e7..220bd9f 100644
--- a/sbin/ifconfig/ifconfig.8
+++ b/sbin/ifconfig/ifconfig.8
@@ -28,7 +28,7 @@
 .\"     From: @(#)ifconfig.8	8.3 (Berkeley) 1/5/94
 .\" $FreeBSD$
 .\"
-.Dd September 2, 2009
+.Dd September 23, 2009
 .Dt IFCONFIG 8
 .Os
 .Sh NAME
@@ -598,7 +598,10 @@ If the interface was reset when previously marked down,
 the hardware will be re-initialized.
 .El
 .Pp
-The following parameters are for ICMPv6 Neightbor Discovery Protocol:
+The following parameters are for ICMPv6 Neightbor Discovery Protocol.
+Note that the address family keyword
+.Dq Li inet6
+is needed for them:
 .Bl -tag -width indent
 .It Cm accept_rtadv
 Set a flag to enable accepting ICMPv6 Router Advertisement messages.
@@ -619,7 +622,10 @@ Clear a flag
 .Cm defaultif .
 .It Cm ifdisabled
 Set a flag to disable all of IPv6 network communications on the
-specified interface.
+specified interface.  Note that if there are already configured IPv6
+addresses on that interface, all of them are marked as
+.Dq tentative
+and DAD will be performed when this flag is cleared.
 .It Cm -ifdisabled
 Clear a flag
 .Cm ifdisabled .