MAC Address

Why does the eathernet address always atart with 00.xx.xx.xx.xx.xx???

It doesn't.

The first 6 digits are the Organizationally Unique Identifier (OUI), which is the number assigned to company for their devices. There are a lot of them that start with 00.xx.xx, but there are a lot that don't. Following are some examples.

00-02-B3 (hex) Intel
00-02-B4 (hex) DAPHNE
00-02-B5 (hex) Avnet, Inc.
00-04-5A (hex) Linksys
02-C0-8C (hex) 3COM
08-00-07 (hex) APPLE

Thank you for your reply, it was a greaty help inunderstanding but still the OUI starts withs 0X.XX.XX ? .Wating for your prompt reply.

The "0" doesn't matter. It is just part of the 6 digit number (just like your phone number or social security number). Here are some examples of companies with no "0".

10-00-5A (hex) IBM
AA-00-00 (hex) DIGITAL
AA-00-01 (hex) DIGITAL
AA-00-02 (hex) DIGITAL