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OT? The "Lifetime" of a MAC Address?

Hello all...

It's my understanding that makers of network cards buy up blocks of MAC addresses to use on their finished cards. (I also understand that some NIC makers have seemingly reused the block they purchased with the--sometimes mistaken--belief that no two adapters would ever "see" one another on the same network segment.)

With the way technology moves on, I got to wondering if there is ever a time when a network card's MAC address is considered to be "free" because the hardware that it was originally assigned to should be long since out of use?

(Why am I wondering about this? Because I run a lot of older networking gear (much of it token ring) and it seemed like something to think about.)

William

Reply to
William R. Walsh
Loading thread data ...

time

use?

gear

MAC address is 6 hexadecimal numbers. Do the math and report back.

Reply to
T Shadow

Well, in fact it's 12 hex numbers ;-) Or 48 bits. It's more a potential problem of lack of administration at the manufacterers side, or errors made by programmers of network drivers.

If you really want to keep things in your own hand, start using self assigned network addresses and do the administration yourself. Half of the total ethernet address space is reserved for locally assigned addresses.

--
Joop van der Velden - pe1dna@amsat.org
Reply to
Joop van der Velden

MAC

NIC

the--sometimes

the

Right. Was in a hurry. Point is, you'd have to be more unlucky than someone who wins the lottery is lucky.

Reply to
T Shadow

On Sun, 05 Nov 2006 04:19:34 GMT, "T Shadow" put finger to keyboard and composed:

MAC

NIC

the--sometimes

the

a

the

of

networking

How many addresses are in a manufacturer's block?

- Franc Zabkar

--=20 Please remove one 'i' from my address when replying by email.

Reply to
Franc Zabkar

48 bits = 12 4 bit hexadecimal words. The forst 24 bits are reserved to uniquely identify the manufacturer. The last 24 bits are for a unique serial number. As such, each "manufacturer" can produce 16,777,215 (2**24 -1) unique serial numbers. If these get used up, then the manufacturer can request/designate another 24 bit prefix and double their MAC address space.

Could you please explain this last statement that "Half of the total Ethernet address space is reserved for locally assigned addresses?" I ask since if this was IPV4 you were referencing, then the only "private" (local) addresses are in the range 10.0.0.0/8 (maximum 16,777,214 adresses),

172.16.0.0/12 (max 1,048,574 addresses), and 192.168.0.0/16 (max 65,534 addresses). This is a maximum total of 17,891,322 unique addresses out of the 4,294,967,296 (2**32) total addresses - about 4% of the total!

Bob

Reply to
Bob Shuman

The only correlation between the MAC address and an IP address is whatever IP you give to it. A network card will have an assigned MAC address that you can choose to ignore or not, in favour of an IP.

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Baron:
Reply to
Baron

NIC

the--sometimes

the

-> Franc Zabkar

More than I remembered. 24bit. Still leaves 16 million + numbers. Have no reason to think a manufacturer can only have one number set. Year estimated to run out of numbers, 2100.

Reply to
T Shadow

Of the first 24 bits, there is 1 bit reserved for broadcast/multicast addresses and 1 bit is reserved for locally assigned ethernet addresses.

We are talking Ethernet addresses here. Not IP addresses.

Ethernet addresses can be self assigned and administered. On every ethernet card the burned-in address can be changed into whatever you want it to be. If you do you should set the LAA bit. (Locally Administered Address)

formatting link 

--
Joop van der Velden - pe1dna@amsat.org
Reply to
Joop van der Velden

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