[Dnsmasq-discuss] RA support in dnsmasq

[Gene Czarcinski]

On 11/30/2012 11:32 AM, Simon Kelley wrote:
> On 30/11/12 15:54, Gene Czarcinski wrote:
>> On 11/29/2012 04:18 PM, Simon Kelley wrote:
>>> On 29/11/12 20:31, Gene Czarcinski wrote:
>>>
>>>> I spoke too quickly.
>>>>
>>>> The cause of the problem is libvirt related but I am not sure what just
>>>> yet.
>>>>
>>>> I was running a libvirt that had a lot of "stuff" on it but seemed to
>>>> work OK. Then, earlier today I update to a point that appears to be
>>>> somewhat beyond the leading edge and, although I was not getting any
>>>> RTR-ADVERT messages, it turned out that there were/are big-time problems
>>>> running qemu-kvm. So, back off/downgrade to the previous version.
>>>> Qemu-kvm now works but the RTR-ADVERT messages are back.
>>>>
>>>> This may be a bit time-consuming to debug!
>>>>
>>> Are you seeing the new log message in netlink.c?
>>>
>>>
>> The good news is that libvirt is working again (I must have done a
>> git-pull in the middle of an update).  Thus, I am not seeing the large
>> numbers of RTR-ADVERT.
>>
>> Yes, I am seeing the new log message and I have a question about that.
>> Every time a new virtual network interface is started, something must be
>> doing some type of broadcast because all of the dnsmasq instances (the
>> new one and all the "old" ones) suddenly wake up and issue a flurry of
>> RA packets and related syslog messages.  To kick the flurry off, there
>> one of the new "unsolicited" syslog messages from each dnsmasq instance.
>>
>> Is this something you would expect?  Is this "normal?"  The libvirt
>> folks they are not doing it.
> I'd expect it. The code you instrumented gets run whenever a "new
> address" event happens, which is whenever an address is added to an
> interface. "Every time a new virtual network interface is started" is a
> good proxy for that.
>
> The dnsmasq code isn't very discriminating, it updates it's idea of
> which interfaces hace which addresses, and then does a minute of fast
> advertisements on all of them. It might be possible to only do the fast
> advertisements on new interfaces, but implementing that isn't totally
> trivial.
>
>
Yes, I doubt very much if it would be trivial.  However, I do not 
believe that this is the basic problem.

When the problem occurs, one of the networks "suddenly" attempts to work 
with the real NIC rather than the virtual one defined in its config 
file.  I slightly changed the IPv4 and IPv6 addresses defined for this 
network and the problem went away.  I have also "just" seen the problem 
happen on another system which also had that virtual address defined.

BTW, these configurations all use interface= and bind-dynamic rather 
than the "old" bind-interface with listen-address= specified for each 
specified IPv4 and IPv6 address.  I had not noticed the problem 
previously.  Why it occurs at all with just this specific address is 
puzzling.

The configuration in which causes problems is:
------------------------------------------
# dnsmasq conf file created by libvirt
strict-order
domain-needed
domain=net6
expand-hosts
local=/net6/
pid-file=/var/run/libvirt/network/net6.pid
bind-dynamic
interface=virbr11
dhcp-range=192.168.6.128,192.168.6.254
dhcp-no-override
dhcp-leasefile=/var/lib/libvirt/dnsmasq/net6.leases
dhcp-lease-max=127
dhcp-hostsfile=/var/lib/libvirt/dnsmasq/net6.hostsfile
addn-hosts=/var/lib/libvirt/dnsmasq/net6.addnhosts
dhcp-range=fd00:beef:10:6::1,ra-only
-------------------------------------------------

When I changed all the "6" to "160", the problem, disappeared.  And 
there is another network defined almost the same with "8" instead of "6" 
and I have had no problems with it.

The real NIC is configured as a DHCP client  for both IPv4 and IPv6.   
It is assigned "nailed" addresses of 192.168.17.2/24 and 
fd00:dead:beef:17::2.

And I just discovered why crazy stuff is happening (but I do not know 
what causes it) ... the P33p1 NIC has:
   inet6 fd00:beef:10:6:3285:a9ff:fe8f:e982/64 scope global dynamic

And the reason why may be related to that NetworkManager goes through a 
verly long dance to bring up an interface.  With dnsmasq autostarted for 
net6, it may have gotten there first ... but it should have not 
responded to p33p1 in any case.  I am getting a little suspicious of 
dnsmasq with bind-dynamic!

Gene