Too-frequent change of privacy address / ND monitoring

[Marco Sommani]

On 27/mar/2013, at 08:47, Erik Kline <ek at google.com> wrote:

> On 27 March 2013 16:31, Fernando Gont <fernando at gont.com.ar> wrote:
> On 03/26/2013 09:29 AM, Marco Sommani wrote:
> > Phil,
> >
> > when everything works according to standards, temporary addresses are
> > regenerated just before the preferred lifetime times out, so you have
> > the possibility to alter the frequency of renewals by changing the
> > preferred-lifetime of the prefix in the Router-Advertisements.
> 
> Privacy addresses will very likely regenerate before such timer expires.
> -- Actually, such timer shouldn't expire if you continue receiving RAs...
> 
> I have in the past seen firewalls that dropped some critical packets but allowed others through (in one case: RS/RA were fine but ND was filtered, which led to IPv4 working in 3 second spurts, i.e. until NUD kicked in).
> 
> Totally random crazy idea: could there be firewalls on some of these machines that are causing multicast RAs to be filtered but unicast RAs are fine (e.g. a unicast RA reply to an RS)?  It could cause a machine to think the network went away after a unicast RA response, re-issue an RS and create a new tempaddr after the "new" unicast RA arrives.


From my experience: I don't know about firewalls, but loss of multicast RAs sometimes is coaused by buggy implementations of igmp-snooping or mld-snooping on Ethernet switches. I have encountered some switches where igmp-sooping blocked all L2 multicasts with destination 33:33:xx:xx:xx:xx.

More recently, I have found switches where mld-snooping blocks all IPv6 multicasts directed to ff02::1. I presume that the implementors did not know that mld-registers are not required for that particular group. As a turn-around, I had to enable explicitly group ff02::1 on all ports via manual configuration.

-- 
Marco Sommani
Consiglio Nazionale delle Ricerche
Istituto di Informatica e Telematica
Via Giuseppe Moruzzi 1
56124 Pisa - Italia
work: +390506212127 (PSTN and nrenum.net)
mobile: +393487981019
fax: +390503158327
mailto:marco.sommani at cnr.it

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