[Openstack] ARP Caching

Rick Jones rick.jones2 at hp.com
Sat Mar 14 21:50:13 UTC 2015


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?

> 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

>
> 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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