netdev - Re: [PATCH] ipv6: addrconf: clear IPv6 addresses and routes when losing link

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Date:	Wed, 27 Oct 2010 13:39:32 -0700
From:	Maciej Żenczykowski <zenczykowski@...il.com>
To:	Lorenzo Colitti <lorenzo@...gle.com>
Cc:	netdev@...r.kernel.org, Brian Haley <brian.haley@...com>
Subject: Re: [PATCH] ipv6: addrconf: clear IPv6 addresses and routes when
 losing link

> The current privacy address comes back because it's a time-based hash.

I would guess it uses jiffies (or some other equally fine-grained
time, or just pulls from a random entropy source),

I see no reason why the second time around it would generate the same
privacy address.
In other words: are you absolutely certain of this?  It's certainly
not how I would expect it to function.

v2.6.36/net/ipv6/addrconf.c
#ifdef CONFIG_IPV6_PRIVACY
#include <linux/random.h>
#endif

and

http://lxr.linux.no/linux+v2.6.36/net/ipv6/addrconf.c#L1608

static int __ipv6_regen_rndid(struct inet6_dev *idev) {
        get_random_bytes(idev->rndid, sizeof(idev->rndid));
        idev->rndid[0] &= ~0x02;

certainly seem to point towards it being totally random.

> I think the old ones are gone. Still, I think it's better that
> connections from 1 day ago don't work any more (the default for
> privacy addresses is 1 day), than if all new and all old connections
> don't work any more.

No, the default is _no more_ than 1 day preferred and 7 days valid.
But those are the upper maximums, the actual values are the
preferred/validity values taken from the RA (limited to whatever the
max limit sysctls are set to).
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