[Bridge] Number of addresses limitation

François Schmidts francois at tiolive.com
Thu Aug 26 15:27:53 PDT 2010


  On 26/08/2010 23:40, Stephen Hemminger wrote:
> On Thu, 26 Aug 2010 23:00:07 +0200
> Nicolas de Pesloüan<nicolas.2p.debian at free.fr>  wrote:
>
>> Le 26/08/2010 21:38, Nicolas de Pesloüan a écrit :
>>> Le 25/08/2010 23:49, François Schmidts a écrit :
>>>>      On 25/08/2010 22:39, Stephen Hemminger wrote:
>>>>> On Wed, 25 Aug 2010 21:43:11 +0200
>>>>> Nicolas de Pesloüan<nicolas.2p.debian at free.fr>     wrote:
>>>>>
>>>>>> Le 25/08/2010 16:51, François Schmidts a écrit :
>>>>>>>        Hi,
>>>>>>>
>>>>>>> I'm using bridge-utils to add a bunch of tap interfaces to my computer
>>>>>>> so I can run different qemu vm at the same time without using nat to
>>>>>>> give them network access. It works fine.
>>>>>>>
>>>>>>> But at the same time I would like to add a lot of IPv6s addresses to the
>>>>>>> bridge interface (br0). I find myself limitated to more or less 56
>>>>>>> addresses. If I add one more, one of the addresses already existing just
>>>>>>> disappear from the br0 interface.
>>>>>>>
>>>>>>> Is there something I could do to remove or extent this limitation ?
>>>>>> Did you try the same IPv6 configuration on a normal ethernet NIC ? Do you think this is a bridge
>>>>>> only related problem ?
>>>>>>
>>>>> Also what tools are you using? Don't use ifconfig (iputils) for IPv6;
>>>>> only ip command (iproute2) works correctly with multiple addresses.
>>>> I use something like "ip addr add<prefix>::number/64 dev br0" in a loop
>>>> to add quickly multiple addresses to the bridge.
>>>> As far as I have tested it on classic interfaces like eth0, it works
>>>> fine and I can see my 200 addresses (if I added 200 of them) in the
>>>> output of ifconfig.
>>> I just tested on a 2.6.32 kernel, and get the following results :
>>>
>>> Whatever interface I use (bridge or normal Ethernet interface), I'm able to add 200 IPv6 address.
>>>
>>> "ifconfig" display all the IPv6 address on the interface.
>>> "ip addr show" only display about 53 of them.
>>>
>>> Can you try and ping the 200 IPv6 address from another host, to know whether this is a real IP
>>> problem or only a display bug. It might be an iproute2 bug on the addr show part.
>> Another test showed that one can ping the 200 addresses. So this really look like an iproute2 or
>> netlink problem, and unrelated to bridge.
>>
> I just put 2000 addresses onto dummy device and the all show up
> with ip addr.  Do you have old tools, the issue is likely the size
> of the buffer in netlink interface between ip command and kernel.
> Current version has 16K buffer, but it could easily be increased.
Thanks for all your answers.

I tested all of this all over again and I couldn't recreate the bug, 
neither on my local machine or on the distant dev server I use for test 
and where the limitation showed up the first time. I added 2000 
addresses on both which were reachable to ping without difficulties.

The problem may have come from a display bug from the tool I used then 
to list IP addresses.

Sorry to have bothered you with an "nonexistent" bug and thanks again.


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