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Media-One Express, IP Masquerading

Rich Braun wrote in a message to Mike Bilow:

> Really, now how did your laptop work on your cable modem? Because like
> well it wouldn't work, because Mediaone uses your ethernet cards internal
> ethernet address ...

 RB> I've heard of devices which are built like that.  I can't
 RB> comment on whether the Media One cable box does that, but I
 RB> know the one supplied by CAI (as noted in my earlier
 RB> posting) doesn't.  If a cable company does hardwire Ethernet
 RB> MAC addresses, then they're going down a very expensive path
 RB> which won't work in the market down the road.

Keep in mind that the so-called "hardwired" address of an Ethernet card is not
really "hardwired" at all.  Software drivers read out the address and then use
it on the wire.  If the driver is told to use some other address, then it will
do as it is told.  In other words, it is trivial to make one Ethernet card fake
the address of any other Ethernet card at will in software.  This is commonly
done for fail-over and other specialized purposes.  The "hardwired" address is
simply a convenient default because it is guaranteed to be unique, but it
provides absolutely nothing for security or authentication.  Do not confuse
security with mere obfuscation.
-- Mike

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