Better not change the cable modem address
 Q:
When you buy a cable modem it comes with its own unique address. The address is
placed on the carton by the manufacturer as a "MAC" address (e.g.
00-90-84-44-5f-33). Can this address be changed? How can this be done? (Michael Microscopist, Cincinnati, Ohio)
A:
Your cable modem manufacturer can change it but only to a valid address. Changes are fraught with peril.
The MAC address, short for Media Access Control address is a hardware address that uniquely identifies each node on a
network. For example, I have a Gateway computer (a node) that uses an RCA cable modem to connect to a local area network
(LAN) run by @home.com, the Internet Service Provider who connects my computer and others on the LAN to the Internet. My cable modem has a unique
hardware MAC address: 00-10-94-11-02-21.
Now, suppose I get RCA to change my MAC address to some arbitrary number that appeals to me, say 00-90-84-44-5f-33 and RCA is willing to do it. That's
your MAC address, as it happens, so you won't be able to access your LAN any more because your unique number identifying you isn't unique any more.
I've stolen it.
That's why Internet conventions (called the IEEE 802 standards) forbid such changes. A modem manufacturer determines a MAC addresses following a
careful set of rules that result in unique identifiers.
The procedure for changes is difficult enough that "in practice, it would never be done," says RCA modem technical support. The technician would need to
de-solder the chip containing the address and then burn in (i.e., rearrange the transistors on the chip using ultraviolet radiation) a new address. Also "it's
slightly shady", says RCA technical support, because, in so doing, you could pretend to be using a cable modem by a different manufacturer than you really
are.
(Answered by April Holladay, science correspondent, August 27, 2001)
Further Surfing:
internet.com: Webopedia, MAC address
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