Linked by Howard Fosdick on Mon 21st Nov 2011 07:48 UTC
Google Last June, CNET disclosed that Google collects and publishes the estimated locations of millions of phones, laptops, and other Wi-Fi devices. All without their owner's knowledge or permission. Google has finally announced how to exclude your home network from this database. Simply append "_nomap" to its name. Details over at CNET. Left unsaid is why the burden is placed on millions of individuals to opt-out, instead of on perpetrator Google.
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RE[3]: Comment by clhodapp
by Alfman on Mon 21st Nov 2011 22:32 UTC in reply to "RE[2]: Comment by clhodapp"
Alfman
Member since:
2011-01-28

Soulbender,

"In practice MAC addresses are not unique (and don't actually have to be)."

I really would like to know what you mean here, because in practice having duplicate MAC addresses will break things like DHCP and switching hubs which rely on a MAC address's uniqueness.

Sometime adapters make it possible to spoof MAC addresses and do ARP spoofing - which can even have legitimate uses like automatic failover, but then original host will stop receiving packets.

"Probably not because it would have been impossible or at least not practically feasible. How would your devices locate each other without a unique, visible address?"

(Didn't you just say it doesn't need to be unique?)

I'm not here to re-engineer it, but the unique id doesn't need to be static between sessions, it just needs to be unique per AP at any given time.

Reply Parent Score: 2

RE[4]: Comment by clhodapp
by Soulbender on Mon 21st Nov 2011 23:14 in reply to "RE[3]: Comment by clhodapp"
Soulbender Member since:
2005-08-18

I really would like to know what you mean here, because in practice having duplicate MAC addresses will break things like DHCP and switching hubs which rely on a MAC address's uniqueness.


Sure, it causes problem..on the local segment. It wont matter one bit if a company in Stockholm and one in Manila have devices with the same MAC address. A MAC does not need to, and in practice sometimes isn't, globally unique. I know some folks who have managed to end up with two different network cards (from the same manufacturer, of course) with the same MAC address.

(Didn't you just say it doesn't need to be unique?)


Yes, it has to be locally unique but not globally.

I'm not here to re-engineer it, but the unique id doesn't need to be static between sessions


You have a point there, it doesn't have to be the same forever. Of course, the problem is how you define a session. Is it the time between reboots of the AP? Individual TCP/IP sessions? As I said, it might be possible but not practically feasible for various reasons. Plus there's also some, very limited, security in knowing what MAC address your AP and workstations has. That said, MAC address security is an administrative burden for anything but tiny home networks and easy to circumvent.

Reply Parent Score: 2

RE[5]: Comment by clhodapp
by Alfman on Tue 22nd Nov 2011 00:33 in reply to "RE[4]: Comment by clhodapp"
Alfman Member since:
2011-01-28

Soulbender,


"A MAC does not need to, and in practice sometimes isn't, globally unique. I know some folks who have managed to end up with two different network cards (from the same manufacturer, of course) with the same MAC address."

I realize that MAC addresses only matter locally, but hardware MAC addresses are intended to be globally unique and manufacturers are not supposed to reuse them. Can you say which manufacturer is reusing addresses and their reason for doing so?


"You have a point there, it doesn't have to be the same forever. Of course, the problem is how you define a session. Is it the time between reboots of the AP? Individual TCP/IP sessions? As I said, it might be possible but not practically feasible for various reasons."

Why is that a problem? A session could be defined as whatever the standard deemed appropriate - including leaving it configurable in firmware. The higher level protocols don't need to be aware of it, there just needs to be a dynamic mapping between them and raw MAC addresses, which we already have as ARP.

Like I said, I wouldn't want to re-engineer 802.11 now that's it's here and working, at least not without a much more compelling reason. But it seems to me that they could/should have avoided the use of unique static identifiers when it was being worked on.

Reply Parent Score: 2

RE[4]: Comment by clhodapp
by phoenix on Tue 22nd Nov 2011 18:41 in reply to "RE[3]: Comment by clhodapp"
phoenix Member since:
2005-07-11

Soulbender,

"In practice MAC addresses are not unique (and don't actually have to be)."

I really would like to know what you mean here, because in practice having duplicate MAC addresses will break things like DHCP and switching hubs which rely on a MAC address's uniqueness.


MAC addresses have to be unique only within the same broadcast domain (ie, subnet). MAC addresses do not have to be unique on separate subnets, even if within the same building.

Most consumer wireless routers will automatically clone the MAC address of the computer it's connected to, using that MAC address on it's WAN interface. You then have two devices in the same location with the same MAC address. But, they are on separate subnets, in separate broadcast domains, so it all works.

Reply Parent Score: 2

RE[5]: Comment by clhodapp
by Alfman on Tue 22nd Nov 2011 21:37 in reply to "RE[4]: Comment by clhodapp"
Alfman Member since:
2011-01-28

phoenix,

"MAC addresses have to be unique only within the same broadcast domain (ie, subnet). MAC addresses do not have to be unique on separate subnets, even if within the same building."

Thank you for the response, I already know how they work though. The hardware MAC is designed to be unique globally, even if it's only necessary to be unique locally. It is not a misunderstanding on my part.

To my knowledge we still haven't needed to recycle them in hardware. If you know of a source that talks about manufacturers reusing MACs, I'd love a link.

http://anonsvn.wireshark.org/wireshark/trunk/manuf

There appear to be plenty of unassigned entries left scattered throughout.

Edited 2011-11-22 21:40 UTC

Reply Parent Score: 2