[Dnsmasq-discuss] RA support in dnsmasq

Simon Kelley simon at thekelleys.org.uk
Fri Nov 30 16:32:20 GMT 2012


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.

Cheers,

Simon.

> 
> Gene
> 
> 
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