Question on 802.11r

[Krishna Chaitanya]

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.

>> 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. Some vendors
like cisco support L3 roaming over wifi using mobile IP.