[Bug 250919] IPV6_PRIVACY=rfc3041 in /etc/sysconfig/networking/devices/ifcfg-eth0 does not take effect

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https://bugzilla.redhat.com/show_bug.cgi?id=250919

--- Comment #46 from Peter Bieringer <pb at bieringer.de> 2011-05-12 03:09:34 EDT ---
I made another interesting experience, which can be the case why it on some
level works and suddenly after upgrading distribution or switching distribution
no longer.

On Scientific Linux 6.0 (=RHEL 6) IPV6_PRIVACY="rfc3041" *works*, but from
known details, the sysctl toggle is switched after ip link set DEV up. So this
behavior is now unexpected.

I digged deeper and found that the toggle switch is no longer successful, if a
10 second sleep is inserted:

--- ifup-ipv6.orig 2010-09-01 16:34:41.000000000 +0200
+++ ifup-ipv6 2011-05-11 16:56:26.391664836 +0200
@@ -142,10 +142,15 @@

 # Enable IPv6 RFC3041 privacy extensions if desired
 if [ "$IPV6_PRIVACY" = "rfc3041" ]; then
+ ip link show dev $DEVICE
+ ip addr show dev $DEVICE
+ sleep 10
  /sbin/sysctl -e -w net.ipv6.conf.$DEVICE.use_tempaddr=2 >/dev/null 2>&1
  if [ $? -ne 0 ]; then
   echo $"Cannot enable IPv6 privacy method '$IPV6_PRIVACY', not supported by
kernel"
  fi
+ ip link show dev $DEVICE
+ ip addr show dev $DEVICE
 fi

 # Setup default IPv6 route, check are done by function


=> the "it works" behaviour is depending on a timinig issue, I assume at least
two possible cases:

- the sysctl toggle is still accepted until first IPv6 negotiation is started
or finished (e.g. router advertisement is received)
- the "ip link set dev DEV up" has some internal delay and if system speed is
fast, the sysctl toggle is set before internal IPv6 initialization.

Anyway, current implementation leads to unpredictable behavior.

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