[avahi] Resolving many ( > 200 ) items seems to lead to apparent congestion in the dbus

[Daniel Wynne]

Hi again!

Is there anyone responsible available who is capable of answering my 
previous question? Everybody on vacation? ;-)

Kind Regards

Daniel



Daniel wrote:
> Hi Folks,
>
> just returning from my summer vacation I reflected about past projects.
>
> Thereby I also wondered about our little conversation concerning Avahi 
> cache sizes.
>
> Trent, you made those promising hints that you will loosen the strict 
> limitations to meet requirements of larger network implementations.
>
> Could you, or any other responsible person please make a definite 
> authorative statement about this issue so we can proceed with development?
> Me and my boss would be very appreciated about this ;-)
>
> Kind Regards
>
> Daniel
>
>
> Daniel wrote:
>   
>> Hi Trent!
>>
>> These are great news for us! :-)
>> We were seriously concerned about the issue, that the Avahi mDNS 
>> implementation prevented us from developing Linux camera management 
>> applications for huge setups.
>>
>> In the following I provide a short calculation to give you a hint of 
>> what we need:
>>
>>     - Right now we have setups with deployments of up to 800 devices We 
>> do not think that deployments with even more devices in one network make 
>> sense, as this already can be considered as a individual feasibility 
>> study. But lets calculate with this worst case scenario and for the sake 
>> of convenience we even round it up to N = 1000 devices per network.
>>
>>     - Since every device typically comes up with 2-3 ip addresses, we 
>> have to reserve cache entries for N*( 3 A's, 1 PTR, 1 SRV, 1 TXT. ) => 
>> AVAHI_CACHE_ENTRIES_MAX >= 6*N = 6000 entries.
>>
>>     - As the dbus limitations are concerned the maximum number of dbus 
>> objects per client will have to be increased, too. Since we have to 
>> create N*3 AddressRecordBrowsers, N*1 ServiceResolver, 1 Client, 2 
>> ServiceBrowsers => OBJECTS_PER_CLIENT_MAX >= 4*N + 3 = 4003 ~ 4000 entries
>>
>> As I do not have that much insight into the Avahi-code there might be 
>> even more limits that might have to be adapted to achieve a coherent 
>> configuration.
>>
>> If you need any additional information, let me know.
>>
>> Thank you Guys for the great support so far!
>>
>> Kind Regards
>>
>> Daniel
>>
>>
>> Trent Lloyd wrote:
>>   
>>     
>>> FWIW, I've always felt this was a little restrictive as well but never  
>>> really ran into it in production.
>>>
>>> I am personally keen on upping them a little - Daniel, can you tell us  
>>> what values seem to work well for you?
>>>
>>> Thanks,
>>> Trent
>>>
>>> On 27/06/2009, at 12:04 AM, Daniel Wynne wrote:
>>>
>>>   
>>>     
>>>       
>>>> Hi Lennart!
>>>>
>>>> After a short interrupt I am back in avahi-business ;-)
>>>>
>>>> PLaying around a little bit with parameters I boiled it down to
>>>> AVAHI_CACHE_ENTRIES_MAX
>>>> OBJECTS_PER_CLIENT_MAX
>>>>
>>>> These Parameters are slightly tight I think when it comes to bigger
>>>> networks i.e. more than 100 Services.
>>>>
>>>> You said these limitations are implemented to avoid misuse, i.e.
>>>> DOS-Attacks.
>>>>
>>>> Do you think it is possible in future releases of Avahi to loosen  
>>>> these
>>>> limitations a little bit, to enable more comprehensive usage of Avahi,
>>>> even for professional applications like ours ;-)
>>>> DOS Attacks are way above the limitations of 500, even way above  
>>>> 5000. I
>>>> think when talking about DOS we are in millions and above.
>>>>
>>>> What do you say?
>>>>
>>>> Kind Regards
>>>>
>>>> Daniel
>>>>
>>>>
>>>>
>>>> On Sun, 2009-06-07 at 01:47 +0200, Lennart Poettering wrote:
>>>>     
>>>>       
>>>>         
>>>>> On Thu, 28.05.09 13:43, Daniel Wynne (daniel.wynne at mobotix.com)  
>>>>> wrote:
>>>>>
>>>>>       
>>>>>         
>>>>>           
>>>>>> But I think thats exactly the problem in our case. In our  
>>>>>> Testnetwork
>>>>>> reside about 250 cameras we want to find and resolve via Avahi. So  
>>>>>> the
>>>>>> cache is way big enough.
>>>>>>         
>>>>>>           
>>>>>>             
>>>>> No. The limit of 500 entries in the cache that Avahi enforces is for
>>>>> RRs, not services or hosts.
>>>>>
>>>>> For each service you need (at least) one A, one PTR one SRV and one
>>>>> TXT RR. Usually even more. I.e. if you register 250 services and want
>>>>> to browser for them all at the same time you need as absolute minimum
>>>>> space for 1000 entries, and practically even more.
>>>>>
>>>>> Lennart
>>>>>
>>>>>       
>>>>>         
>>>>>           
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>>>> http://lists.freedesktop.org/mailman/listinfo/avahi
>>>>
>>>>     
>>>>       
>>>>         
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>>>     
>>>       
>>   
>>     
>
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