Question on 802.11r

[Krishna Chaitanya]

On Tue, Nov 12, 2013 at 3:58 PM, Nicolas Cavallari
<Nicolas.Cavallari at green-communications.fr> wrote:
> On 12/11/2013 11:19, Krishna Chaitanya wrote:
>> On Tue, Nov 12, 2013 at 3:46 PM, Nicolas Cavallari
>> <Nicolas.Cavallari at green-communications.fr> wrote:
>>> On 12/11/2013 11:08, Krishna Chaitanya wrote:
>>>> On Tue, Nov 12, 2013 at 3:35 PM, Nicolas Cavallari
>>>> <Nicolas.Cavallari at green-communications.fr> wrote:
>>>>> On 12/11/2013 10:19, Antonio Quartulli wrote:
>>>>>> On Tue, Nov 12, 2013 at 08:54:55AM +0000, michael-dev wrote:
>>>>>>> Hi,
>>>>>>>
>>>>>>> Am 12.11.2013 05:36, schrieb Ben Greear:
>>>>>>>> Now, I have a somewhat related question:  Should the station
>>>>>>>> re-acquire DHCP lease after successfully roaming? ...
>>>>>>>> So, it would be nice to skip
>>>>>>>> DHCP, but I'm not sure if that is how real-world networks
>>>>>>>> are configured?
>>>>>>>
>>>>>>> even without 802.11r when devices are roaming within the same SSID, some
>>>>>>> don't refresh DHCP after changing the BSSID. I believe a recent version
>>>>>>> of MAC OS was doing so and maybe others, though I'm not sure which HW/SW
>>>>>>> exactly was used on client side. So that is why I built DHCP-Snooping /
>>>>>>> IP+ARP-Filter on my APs in a way that those stations don't loose network
>>>>>>> connectivity.
>>>>>
>>>>> When devices roams, they expect that the layer2 environment is the same.
>>>>> They are not required to refresh any DHCP lease or anything.
>>>>
>>>> How does the STA knows whether it had done a L2/L3 roaming?
>>>
>>> In 802.11r, the STA initiates the roaming, so it knows.
>>
>> STA has no idea of the topology of the network.
>
> A STA scan the nearby AP, and chooses the best one with the same SSID and security
> setting.  This nearby AP *should* belong to the same L2 network (of course, it's not
> guaranteed, especially with access point with no security).
>
>>
>>>> Only way it can know is if it tries to renew the IP and gets a NACK from
>>>> server, then it things subnet is changed (from NACK) and tries to do
>>>> a full DHCP handshake.
>>>
>>> 802.11 Roaming is always layer 2.  If you have two AP with the same SSID and security
>>> parameters, it mean they belong to the same ESS, so to the same layer 2 network.
>>>
>>> If you want to do a layer 3 roaming, just disconnect and reconnect.  Or use different SSIDs.
>>
>> That's now true, there is no rule that entire ESS must be in the
>> single L2.
>
> See 802.11-2012 4.3.4.2.  Roaming must be transparent to the LLC layer.

Dont change the wording :-).

"STAs within an ESS may communicate and mobile STAs *may* move from
one BSS to another (within the same ESS) transparently to LLC."

It doesnt mandate, but it allows.

may: "The word may is used to indicate a permissible action"