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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/3658e1015a2f7cb7c321cc1a0adfda37757fd80b/nova/network/linux_net.py#L764


On Fri, Mar 13, 2015 at 2:00 PM, Georgios Dimitrakakis <giorgis at acmac.uoc.gr
> 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 hasn't 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 it's 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?
>>>
>>
>> I'm very much *not* an expert in this area, so I'm afraid I'm 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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