[Commotion-dev] static BSSID?

Fri May 18 21:04:42 UTC 2012

Hey folks,

Talked about this with Hans today. We came up with the following algorithm:

BSSID = MD4(ESSID)[0:4] ++ channel 2-byte integer

This is read in English as: "The six byte BSSID is the first four
bytes of the MD4 hash of ESSID concatenated with the lowest two bytes
of the channel."

The rationale for this is that MD4 is uniformly distributed, and the
first four bytes of MD4 are presumably uniformly distributed. (Should
be distributed enough.) Then add on the bytes of the channel so that
same ESSIDs don't collide. MD4 was an arbitrary function choice, and
security is not an issue. :)

I found a public domain implementation of MD4
<http://openwall.info/wiki/people/solar/software/public-domain-source-code/md4>
and made a simple get_bssid() function the same as the above algorithm
(attached).

Signature for get_bssid:

get_bssid(char *essid, unsigned int channel, unsigned char *bssid) //
(result goes in bssid)

Not sure how to add this in, so hope one of you goes ahead and does
that, or let me know how I can be of further service.

Sean

On Thu, May 17, 2012 at 4:23 PM, L. Aaron Kaplan <aaron at lo-res.org> wrote:
>
> On May 17, 2012, at 10:12 PM, Hans-Christoph Steiner wrote:
>
>>
>> If you have multiple mesh nodes radiating on the same frequency in the same area, so that the radio waves overlap, is there ever a time with an OLSR mesh
>> where it would be preferable to have those nodes on separate BSSIDs?  That's the case I'm talking about.
>>
> Yes, you actually could think about that.
> Why? Because you limit the number of neighbors this way. And then you get smaller OLSR  packets.
>
> But in general: if the density of nodes on the same frequencies is too high, then you are in trouble. No matter which protocol.
>
>> For Ad-hoc networks, if your neighbor happens to be radiating on the same frequency, that doesn't mean you want to your ad-hoc network to merge with theirs.
> Exactly!
>
>> That would cause confusion with DHCP servers, different IP ranges and devices on the network, different internet connections, etc.
>>
> ACK.
>
> Ok, maybe I misunderstood you and was just nit-picking on one particular sentence.
>
>> .hc
>>
>> On May 17, 2012, at 11:16 AM, L. Aaron Kaplan wrote:
>>
>>> Maybe we mean the same thing but it came across differently or I am simply nit-picking now.
>>> But as it is written here:
>>> "what I can see since more mesh nodes on the same SSID mean a better network"
>>>
>>> is  not true
>>>
>>> I would say the more nodes on *different* channels but somehow connected to each other (LAN), the better the network.
>>>
>>> Use cable whenever you can :) It keeps those darn radio waves contained hehe.
>>>
>>> I think I have a very very neat solution for this. Can show it to you next time we meet.
>>>
>>> a.
>>>
>>> On May 13, 2012, at 4:08 AM, Hans-Christoph Steiner wrote:
>>>
>>>>
>>>> My guess is that this is not a good idea to include in the madwifi driver, since it goes against how the Ad-hoc standard is supposed to work, and it would hinder interoperability with other implementations outside of madwifi (other Linux drivers, Windows, BSD, Mac OS X, etc.)
>>>>
>>>> But for mesh use, this makes perfect sense from what I can see since more mesh nodes on the same SSID mean a better network, versus with standard Ad-hoc, multiple networks with the same SSID would mean interference, both on the wifi level, and things like multiple DHCP servers, etc.
>>>>
>>>> .hc
>>>>
>>>> On May 12, 2012, at 9:57 PM, Josh King wrote:
>>>>
>>>>> BSSID in an ad-hoc network definitely should be statically set in order
>>>>> to avoid network cell partitioning problems. I remember that hashing
>>>>> the SSID was a proposed solution for this in the madwifi driver, but I
>>>>> don't know if it was ever implemented (I vaguely recall some objection
>>>>> to this as a bad idea, but I cannot for the life of me find the
>>>>> reference to that argument, or think myself of why it might not be a
>>>>> good idea). In any event, there's an old patch posted for the madwifi
>>>>> driver that provides some sample code that could provide some guidance
>>>>> w/ respect to hashing:
>>>>>
>>>>> http://permalink.gmane.org/gmane.linux.drivers.madwifi.devel/4787
>>>>>
>>>>> On Sat 12 May 2012 09:02:40 PM EDT, Jeremy Lakeman wrote:
>>>>>> No, we haven't chosen a hash function at all.
>>>>>>
>>>>>> On Sun, May 13, 2012 at 3:27 AM, Hans-Christoph Steiner
>>>>>> <hans at guardianproject.info> wrote:
>>>>>>>
>>>>>>> That's a really nice, tight idea.  I like it.  Do you have an algorithm for it yet?
>>>>>>>
>>>>>>> .hc
>>>>>>>
>>>>>>> On May 11, 2012, at 10:06 PM, Jeremy Lakeman wrote:
>>>>>>>
>>>>>>>> I propose that the BSSID is generated as a hash of the SSID. This way
>>>>>>>> each mesh network will have a unique, but static BSSID without needing
>>>>>>>> the user to know it.
>>>>>>>>
>>>>>>>> On Sat, May 12, 2012 at 3:33 AM, Hans-Christoph Steiner
>>>>>>>> <hans at guardianproject.info> wrote:
>>>>>>>>>
>>>>>>>>> The trickiest thing for the user of the OlsrMeshTether app remains the ad-hoc network associating.  If a bunch of phones are starting up at the same time, they can easily start associating with themselves in clusters.  Then there is multiple meshes that can't talk to each other.
>>>>>>>>>
>>>>>>>>> It seems a simple solution to this is to just hard-code the BSSID for Commotion in general as a default, then allow people to change this if they really want to.  I propose using CC:CC:CC:CC:CC:CC as the static BSSID.
>>>>>>>>>
>>>>>>>>> Is there any reason why we wouldn't want to use a static BSSID as the default?
>>>>>>>>>
>>>>>>>>> .hc
>>>>>>>>> _______________________________________________
>>>>>>>>> Commotion-dev mailing list
>>>>>>>>> Commotion-dev at lists.chambana.net
>>>>>>>>> http://lists.chambana.net/mailman/listinfo/commotion-dev
>>>>>>>>>
>>>>>>>
>>>>>>
>>>>>> _______________________________________________
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>>>>>>
>>>>>
>>>>> --
>>>>> Josh King
>>>>>
>>>>> "I am an Anarchist not because I believe Anarchism is the final goal,
>>>>> but because there is no such thing as a final goal." -Rudolf Rocker
>>>>>
>>>>
>>>>
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>>>> Commotion-dev at lists.chambana.net
>>>> http://lists.chambana.net/mailman/listinfo/commotion-dev
>>>>
>>>
>>
>
>
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