From mboxrd@z Thu Jan  1 00:00:00 1970
From: Lorenzo Colitti <lorenzo@google.com>
Subject: Re: [PATCH] ipv6: addrconf: clear IPv6 addresses and routes when
 losing link
Date: Thu, 28 Oct 2010 15:23:29 -0700
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Cc: netdev@vger.kernel.org, Brian Haley <brian.haley@hp.com>
To: =?ISO-8859-2?Q?Maciej_=AFenczykowski?= <zenczykowski@gmail.com>
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On Wed, Oct 27, 2010 at 1:39 PM, Maciej =C5=BBenczykowski
<zenczykowski@gmail.com> wrote:
> static int __ipv6_regen_rndid(struct inet6_dev *idev) {
> =C2=A0 =C2=A0 =C2=A0 =C2=A0get_random_bytes(idev->rndid, sizeof(idev-=
>rndid));
> =C2=A0 =C2=A0 =C2=A0 =C2=A0idev->rndid[0] &=3D ~0x02;
>
> certainly seem to point towards it being totally random.

It's random, but the random interface ID is a property of the
interface, not of the address, and thus survives interface up/down:

# ip -6 a li dev wlan0 secondary
3: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qlen 1000
    inet6 2620:0:1000:fd01:952f:2586:ed6f:408c/64 scope global
secondary dynamic
       valid_lft 604363sec preferred_lft 85363sec
# ip link set wlan0 down
# ip -6 a li dev wlan0 secondary
# ip link set wlan0 up
# ip -6 a li dev wlan0 secondary
3: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qlen 1000
    inet6 2620:0:1000:167d:952f:2586:ed6f:408c/64 scope global
secondary dynamic
       valid_lft 604799sec preferred_lft 85799sec