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[Openstack] ARP packets not sent during migration


Hi Brian,

yes, you're right, that's the point, libvirt is sending gARPs too 
early.... am I misconfiguring something? Seems to me a really strange 
behaviour...

Ramon


Il 21/03/18 22:35, Brian Haley ha scritto:
> On 03/20/2018 12:40 PM, Ramon Orru wrote:
>> Hello everybody, I'm running a fresh queens cluster. I'm using 
>> bridges to support networking. I'm facing an issue when an instance 
>> is live migrated.
>> Suppose we have an instance running with an interface on vlan XXX, 
>> and we want to migrate it to compute host YYY. We'll call that 
>> instance ZZZ.
>> If no other instance is already running on YYY using vlan XXX, no 
>> bridge called 'br-vlan.XXX at br-vlan' exists yet on YYY.
>> Now, if I migrate ZZZ on YYY host, a new bridge 'br-vlan.XXX at br-vlan' 
>> will be created.
>> During the migration process, ZZZ become unreachable while interfaces 
>> are going up on YYY (from 10 seconds to about 2 minutes).
>> After some troubleshooting, we spotted the problem: bridge 
>> 'br-vlan.XXX at br-vlan' is being created after gratuitous ARP packets 
>> are sent from migrating machines to advise other devices about new 
>> position.
>> The result is: no other device can reach the fresh migrated machine 
>> until ARP table becomes stale.
>> This does not happen when an instance with an interface on same vlan 
>> is already runnning on destination host ('br-vlan.XXX at br-vlan' is 
>> already up and running, and ARPs can be sent flawlessly).
>>
>> Any idea of how to get rid of this? I think it's very unlikely that 
>> I'm the first to face this problem, but i didn't manage to find 
>> additional info on this strange behaviour.
>> Thanks in advance.
>
> Just to clarify - are you talking about connectivity to the floating 
> IP or just on the VLAN itself, i.e. the instance is directly connected 
> to the VLAN.  I'm thinking it's the latter, which would mean it's 
> libvirt(?) sending the gARPs before the bridge is up?
>
> -Brian