[Openstack] ARP Caching

Georgios Dimitrakakis giorgis at acmac.uoc.gr
Fri Mar 13 11:54:22 UTC 2015


> 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? How often is it sending the ARP 
 request?

 Does it send it every time nova configuration is changing?


 Best,


 George




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