[opendtv] Re: Twang's Tuesday Tribune (Mark's Monday Memo)
- From: Mike Enright <menright1@xxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Tue, 04 May 2004 20:15:08 -0700
Craig Birkmaier wrote:
>At 10:22 AM -0700 5/4/04, Kon Wilms wrote:
>
>
>>[...]Of the 6 bytes in a mac address, the first 3
>>represent the manufacturer id. The manufacturer must randomize the last 3
>>for device rollout. With a range of 3 bytes, there is bound to be
>>duplication (you can't even roll out a decent amount of receivers without
>>using up every number). Many manufacturers cut corners in manufacturing and
>>use a random number generator but do not check against a known list of ids
>>previously created.
>>
>>
I just want to point out that there out to be 16 million or so unique
values for the 3 byte field (allowing even for the possibility that some
of the possible values are illegal). So are all the manufacturers
releasing 16 million network cards?
>>Plus, you can change the MAC address on most boards (datacast receivers are
>>notorious for allowing you to do this).
>>
>>So its not so useful for targeting or ensuring data only reaches one
>>
>>
>recipient.
>
>Thanks!
>
>Doesn't IPV6 deal with these shortcomings?
>
>
IPV6 on the one hand allows for a great many addresses to be assigned.
The address field in IPv6 is 128 bits. On the other hand, and
ironically, there is the possibility that if two cards with the same MAC
address were in the same site, they could end up with the same
global-scope IPv6 address. Briefly, the 48-bit MAC address is converted
to a 64-bit interface ID by concatenating a fixed 16-bit value and then
the 64-bit network number is concatenated.
See this tutorial: http://www.ipv6style.jp/en/tech/20030120/index.shtml
and if that one is too abstract, perhaps this Windows-XP oriented one
will help: http://www.ipv6style.jp/en/tryout/20030120/index.shtml
--
Mike Enright
mail: michaelt@xxxxxxxxxxxx AIM: enr Yahoo: michaeltenright
Beautiful Cardiff-by-the-Sea, California
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