IPv6: "xxx::x already configured" in logs... why?

[Lawrence Stewart]

On 29/03/2017 21:49, Rui Paulo wrote:
> On Wed, 2017-03-29 at 21:46 -0500, Lawrence Stewart wrote:
>> [resurrecting an old thread]
>>
>> On 19/06/2014 23:08, Hiroki Sato wrote:
>>> Larry Rosenman <ler at lerctr.org> wrote
>>>   in <20140619140801.GA65420 at thebighonker.lerctr.org>:
>>>
>>> le> > le> Ideas? (I may be an idiot, so any criticism welcomed).
>>> le> > le>
>>> le> > le> if you need the 1841's config, I can supply that as
>>> well.  It's using a Hurricane
>>> le> > le> electric Tunnel.
>>> le> >
>>> le> >  How frequent were the log message added into
>>> /var/log/messages?  And
>>> le> >  when did it start to happen after boot.  Just after lagg0 is
>>> le> >  configured?
>>> le> >
>>> le> > -- Hiroki
>>> le> Looks like:
>>> le>
>>> le> Jun 12 07:00:01 thebighonker kernel: in6_ifadd:
>>> 2001:470:1f0f:3ad:223:7dff:fe9e:6e8a is already configured
>>>
>>>  Thank you.  Three more questions:
>>>
>>>  1. output of "ifconfig lagg0", "ifconfig bce0", and "ifconfig
>>> bce1".
>>>
>>>  2. output of "netstat -s -i".
>>>
>>>  3. output of "ndp -p".
>>>
>>>  The cause of the message is that the automatically-configured
>>> address
>>>  is not recognized as "configured" one and FreeBSD IPv6 stack is
>>>  trying to add it every time a Router Advertisement message is
>>>  received.  I am still not sure why it happened, but the above
>>> three
>>>  would help for further investigation.
>>
>> I've recently set up a VPS with v6 and am seeing the same "in6_ifadd:
>> <v6_addr> is already configured" messages in response to periodically
>> received router advertisements every 5-10 mins. The host is a KVM-
>> based
>> virtual machine with vtnet-based NIC. v6 is fully functional with the
>> statically assigned v6 address, but the spam in /var/log/messages is
>> annoying.
>>
>>
>> FreeBSD revision:
>>   FreeBSD lauren 12.0-CURRENT FreeBSD 12.0-CURRENT #0 r315059: Sun
>> Mar
>> 12 20:44:50 AEDT 2017
>> root at builder-head-amd64:/usr/obj/lauren/usr/src/sys/GENERIC-
>> NODEBUG  amd64
>>
>>
>> Relevant bits from /etc/rc.conf:
>>   rtsold_enable="YES"
>>   ipv6_activate_all_interfaces="YES"
>>   rtsold_flags="-aF"
>>   ifconfig_vtnet0_ipv6="inet6 <v6_addr> prefixlen 64"
>>
>>
>> Interface:
>>   vtnet0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0
>> mtu 1500
>>
>> options=6c07bb<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,VLAN_H
>> WCSUM,TSO4,TSO6,LRO,VLAN_HWTSO,LINKSTATE,RXCSUM_IPV6,TXCSUM_IPV6>
>>         ether <mac>
>>         inet <v4_addr> netmask 0xfffffe00 broadcast <v4_bcast>
>>         inet6 <v6_linklocal>%vtnet0 prefixlen 64 scopeid 0x1
>>         inet6 <v6_addr> prefixlen 64
>>         nd6 options=23<PERFORMNUD,ACCEPT_RTADV,AUTO_LINKLOCAL>
>>         media: Ethernet 10Gbase-T <full-duplex>
>>         status: active
>>
>>
>> I would have thought rtsold should be able to play nice with
>> statically
>> assigned v6 addresses... any ideas?
> 
> Hmm, why would it?  If you setup an IPv6 address and then there's a
> router solicitation advertising the same address, the log message makes
> sense.
> 
> I don't think you should run rtsold if you have a static IPv6 address.

How would the host learn about router(s) on the network and other
addresses it might want? (In my particular environment, I'm pretty sure
they don't change so could be statically configured, but interested in
understanding if (and why) these are mutually exclusive modes of operation).