Is it legal to have a dynamic MAC address?

Of course.

Sure, but it may not be wise -- the idea with MAC IDs is that they're supposed to be 100% unique so that it's possible to route data to a given device with no ambiguity. Hence, if you just randomly choose a MAC ID at boot, sooner or later you'll probably get the same one as some other device on your network, which will likely make both devices malfunction. If you do this in, e.g., a corporate environment, you can bet you're going to get a rather stern talking to after the IT guys track down your rogue hardware.

Most major network cards do allow you to manually set the MAC ID to whatever you like. This is often useful during software development, and one common use in the early days of cable modems was to allow a router to talk to a cable modem: Some cable companies intially wanted to charge for access on a "per computer" basis, so the modem would "lock" itself to the first MAC ID it saw. When a router was then added, while one could call the cable company to get the lock reset, as a practical matter it was often easier to just have the router clone the MAC ID of the device the modem was already locked to (and note that in this specific scenario there's no potential for devices to malfunction, because the two devices with the same MAC ID are on the two different sides of the router).

---Joel

I think you need the latest Windows update for that "feature". :)

In my experience, nothing (OK, well, almost nothing) is more random than the operation of most Microsoft software. Don't see why a MAC address should be any different.

That depends very much what you mean by "legal". I can think of at least three meanings:

(1) Complies with all of the technical requirements for the 801.11 wireless networking specifications. (2) Does not contravene any local, state, Federal, international, or intergalactic trans-dimensional laws which apply in the location where it's being used. (3) Does not break any "acceptable use" policies of the networks on which it is being used. Many WiFi cards do have the ability to accept a new MAC address via software, either before or during operation. No, I won't tell you which ones.

In many cases, how you actually use that capability (i.e. your intent and your actual actions) would likely govern whether this was "legal" or "illegal". It's like possession of things like knives and lock-picks... having them under some circumstances would be quite legal, while having exactly the same things on your person under other circumstances could result in a multi-year visit to prison for possession of a deadly weapon, burglar's tools, and so forth.

Your previous question (about a laptop with no nonvolatile memory at all), added to this one, makes me mildly suspicious that you're trying to put together a laptop which is optimized for network "cracking" and cyber-espionage, and which automatically erase the evidence of same as soon as its power was turned off.

If that's what you're thinking of, then you're getting into "possession of burglar's tools" territory... get caught with such a machine and the boot CD under the wrong circumstances and you might end up facing serious charges.

Only until you find several of his devices on the same network and find he's using a fixed seed value for his random number generator so they sit there and collide in lock-step.

:-)

But you're right, "sooner or later" is realistically "much, much later."

It's still not a good idea to willy-nilly randomly generate your MAC ID, though!

If I recall correctly, the 48-bit MAC address space is formally broken into two sub-classes, based on the setting of one particular bit.

If that bit is zero, then the whole 48-bit address is supposed to be globally unique... the first three bytes include the unique identifier for the organization which "owns" a range of MAC addresses, and the last three bytes give the device-specific number within that organization's number space.

If the bit is one, then it's a "locally administered" MAC address... it doesn't have to be globally unique (i.e. could be randomly generated) and the local network administrator is responsible for assigning such addresses and avoiding any collisions on the local network.

Anybody who is going to generate "locally administered" addresses at random, on the system itself, really ought to have some sort of confirmation protocol to make sure that nobody else on that network is using the chosen address. This would not be easy to do with very high reliability.

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Really? With 48 bits to play with, I would assume your chances are pretty slim... :>

As I recall it's broken into fields for the manufacturer's number, sequential number, etc.

Agreed, I've ready that in the real world many MAC IDs have been used more than once.

Well, all the Intel-based cards that I've checked do. I used the feature once in the past within a company where the DHCP server have IP reservations based on MAC IDs, and in upgrading to a new computer the IT guys said just to change the MAC ID manually until they got around to putting a new entry in their DHCP server's database.

Apparently Windows can do it even if the Ethernet card's driver doesn't natively support the feature:

It was so common that most "home" routers (e.g., those from Netgear/D-Link and similar) today have a "MAC spoofing" option like this. (See, e.g.,

---Joel

The reason I want an NVRAM-free laptop and a totally-dynamic MAC address is because I'm angry at society. I'm angry at society for making irrational rules [such as painful dress codes in the workplace]. I want to take revenge against society by saying the most taboo things in chat rooms without getting into any trouble. I'm not going to tell you what I'd like to say in those chat rooms but I will tell you that it is so dirty, that anyone seeing my text will want to drag me in to the middle of the street and burn me alive while a lynch mob laughs at my painful execution.

I don't wish to say or do anything illegal, just stuff that's so unacceptable-by-societal-norms that the vigilantes would want to dump me in a yellow-hot lava lake.

If my laptop does not store evidence of this and my MAC is dynamic, then I can pretty much write all the puke I want on the internet, and it will be VERY difficult for society to link my identity with my profile.

The stuff I would like to write in chat rooms is totally-legal, non-violent, non-threatening, and non-offensive. However, it's extremely filthy. Any human being reading that stuff would hate my guts. That is why I need this protection.

I want to retaliate against society without getting busted in return.

Also, I want my NIC to have the most powerful transmitter allowed by law and the most sensitive receiver possible. That way I can legally use the internet via the open free wireless access point of public internet cafe [such as those in coffee shops] that are about 1/4 mile away from me. There is a coffee shop near my residence that currently provides free internet access. People living in the apartments nearby can use that access point provided they have a sensitive-enough receiver and a strong-enough transmitter.

I really care about my privacy and security but I have no respect for society's irrational rules. I want to punish society with my perverse words without being burnt to death by society.

--------------------------------------- Posted through

A good antenna will buy you a lot more here than eeking the last few dB out of a receiver or transmitter. Google knows lots of about high-gain WiFi antennas...

I rather doubt you can say anything in an anonymous chat room that's truly going to make anyone feel punished...

Yes, good point!

Agreed. I have a tiny fragment of an OUI that is "mine" that I use here. But, since most of these devices are not "visible" outside these four walls, it's a moot point.

I wonder what folks do when developing devices... (?)

Yes. See:

Go to the above site and type in *your* MAC and see who made

Yes.

That is probably why you willy nilly CAN'T.

Sheesh.

Check your PC's clock, dufus.

You did not "recall" asswipe, you were told about it in this very thread.

May not be as likely as you think.

No router even needs to "do it" since NOTHING can see the connections on that side of the router. Especially when it is a DHCP server, which nearly all are. IF you assign hard IP addresses to your local machines, you are a nut to begin with, especially if you pass that hard IP through the router.

This guy needs to be introduced to lead, moving at a high rate of speed.

I am angry at members of society that are as stupid as you obviously are.

You are even more stupid than Misty Croslin, and she was "affected" by those she "grew up" around in that lame neighborhood that her and her drug crazed bo participated in the degradation of.

Yeah, it is called an intranet.