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Based on the code, it sends the gratuitous ARPs only when the floating IP
is assigned to the VM, and it's sent as many times as the user decided by
configuring the "send_arp_for_ha_count" parameter in nova.conf

So, to be safe, I would add the following in nova.conf and restart nova
services.

send_arp_for_ha=true
send_arp_for_ha_count=20





On Fri, Mar 13, 2015 at 2:54 PM, Georgios Dimitrakakis <giorgis at acmac.uoc.gr
> wrote:

> George,
>
> how often does it send the gratuitous ARP requests?
>
> Does it send it every time a network change is happening?
>
>
> Best,
>
> George
>
>
>  You have to set two variables in the nova.conf file apparently
>> ("send_arp_for_ha" and "send_arp_for_ha_count"):
>>
>>
>> https://github.com/openstack/nova/blob/3658e1015a2f7cb7c321cc1a0adfda
>> 37757fd80b/nova/network/linux_net.py#L764
>> [4]
>>
>> On Fri, Mar 13, 2015 at 2:00 PM, Georgios Dimitrakakis  wrote:
>>
>>  On 03/13/2015 05:54 AM, Georgios Dimitrakakis wrote:
>>>>
>>>>  On 03/12/2015 06:24 PM, Georgios Dimitrakakis wrote:
>>>>>>
>>>>>>  Hello!
>>>>>>>
>>>>>>> I am facing a rather weird issue and would like to know if
>>>>>>> anyone has
>>>>>>> faced it before and the way you have solved it (if any).
>>>>>>>
>>>>>>> Firstly, I d like to let you know that I am running
>>>>>>> Icehouse with Nova-Legacy
>>>>>>> Networking.
>>>>>>>
>>>>>>> I have an application that launches and terminates VMs very
>>>>>>> frequently and
>>>>>>> automatically assigns to them
>>>>>>> floating IP addresses.
>>>>>>>
>>>>>>> As a result if an IP has been used once then the second
>>>>>>> time that is being used
>>>>>>> cannot be reached for at
>>>>>>> least 20minutes (this is the time frame if the newly
>>>>>>> launched VM gets the same
>>>>>>> IP address from one that
>>>>>>> has just been terminated). Furthermore, this issue only
>>>>>>> happens when the second
>>>>>>> VM is launched on a
>>>>>>> different physical node (hypervisor) than the first one.
>>>>>>>
>>>>>>> I believe that I have identified the problem to be ARP
>>>>>>> Caching on the router
>>>>>>> side since if I do:
>>>>>>>
>>>>>>> arping -U -I {Interface-Name} {IP-Address}
>>>>>>>
>>>>>>> in order to update the ARP Caches of the neighbors
>>>>>>> immediately the new VM can be
>>>>>>> reached on its floating
>>>>>>> IP address.
>>>>>>>
>>>>>>> Is this the proper way of solving it?
>>>>>>>
>>>>>>> Can I somehow "instruct" OpenStack not to use the first
>>>>>>> available IP address
>>>>>>> everytime but on a random order
>>>>>>> or the one that hasnt been used for enough time?
>>>>>>>
>>>>>>> Any other thoughts?
>>>>>>>
>>>>>>
>>>>>> Just a thought, have you tried enabling "send_arp_for_ha" in
>>>>>> nova.conf?
>>>>>>
>>>>>> Chris
>>>>>>
>>>>>
>>>>> Hi Chris! Thx for the feedback!
>>>>>
>>>>> send_arp_for_ha = True
>>>>>
>>>>> is already enabled in all nodes (controller and compute).
>>>>>
>>>>> Can I somehow verify that its working?
>>>>>
>>>>
>>>> You should be able to verify with a packet sniffer somewhere on
>>>> your network.
>>>>
>>>>  How often is it sending the ARP request? Does it send it every
>>>>> time nova configuration is changing?
>>>>>
>>>>
>>>> Im very much *not* an expert in this area, so Im afraid Im not
>>>> the
>>>> right person to ask about that.
>>>>
>>>> Chris
>>>>
>>>
>>> Chris,
>>>
>>> thanks for the feedback. Any idea on what to sniff for?
>>>
>>> George
>>>
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>>
>>
>>
>> Links:
>> ------
>> [1] http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack
>> [2] mailto:openstack at lists.openstack.org
>> [3] http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack
>> [4]
>>
>> https://github.com/openstack/nova/blob/3658e1015a2f7cb7c321cc1a0adfda
>> 37757fd80b/nova/network/linux_net.py#L764
>> [5] mailto:giorgis at acmac.uoc.gr
>>
>
>
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