[Openstack] ARP Caching

Georgios Dimitrakakis giorgis at acmac.uoc.gr
Sat Mar 14 22:32:10 UTC 2015


 Hello again Rick!


> On 03/13/2015 06:25 PM, Georgios Dimitrakakis wrote:
>> If I do an :
>>
>> arping -U -I etho x.x.x.x
>>
>> where x.x.x.x is the IP address.
>>
>> I can almost immediately access them outside of the subnet!
>
> I had forgotten that,  Still is that the very same set of options the
> OpenStack code uses?


 I am not aware about that and I would like to know!
 What does Openstack does and how ofted does it send the gratuitous ARP 
 request?



>
>> Do you mean that OpenStack is sending a gratuitous ARP for all
>> and the router is ignoring them unless it is for a specific IP 
>> address?
>>
>> If this is the case is there anything I can do?
>
> I will second the suggestion of getting a packet trace to see just
> what sort of ARP traffic the compute node(s) send and then compare
> that with the documentation for your router.
>
> rick
>


 I will try to see if I can get anything but the problem is that the 
 datacenter
 hosting the facility is in Japan and there is a huge gap communicating 
 with them
 (actually there is no communication).

 If I could only find out what does the router accept would be very nice 
 :-)


 Best,

 George


>>
>> Regards,
>>
>> George
>>
>>
>>> On 03/13/2015 04:55 PM, Georgios Dimitrakakis wrote:
>>>> The value is 10
>>>>
>>>> Do you believe that it should be bigger?
>>>
>>> These accesses of instances which are being delayed by 20 minutes -
>>> are they delayed for other instances in the subnet, or just for
>>> accesses from outside the subnet (ie through a real router)?
>>>
>>> There may be some rather "conservative" routers out there which 
>>> might
>>> not accept gratuitous ARPs, considering it more secure to ARP for
>>> those IPs explicitly itself.
>>>
>>> rick jones
>>>
>>>
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>>
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>
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