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I have a Motorola modem, and when I connect to 192.168.100.1 (modem IP) I see 5 MAC addresses:

  • HFC MAC Address,
  • CPE USB MAC Address,
  • Known CPE MAC Addresses (4), of which one has status SELF and is the same as the HFC MAC Address, and the others have status LEARNED.

What do all of these MAC addresses mean?

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It means you have to accept some answers before asking more questions. –  PeeHaa Jan 10 '11 at 20:26
    
After that go to superuser / serverfault. –  PeeHaa Jan 10 '11 at 20:26
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migrated from stackoverflow.com Jan 10 '11 at 20:37

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4 Answers

A Media Access Control address (MAC address) is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used for numerous network technologies and most IEEE 802 network technologies including Ethernet. Logically, MAC addresses are used in the Media Access Control protocol sub-layer of the OSI reference model.

MAC addresses are most often assigned by the manufacturer of a network interface card (NIC) and are stored in its hardware, the card's read-only memory, or some other firmware mechanism. If assigned by the manufacturer, a MAC address usually encodes the manufacturer's registered identification number and may be referred to as the burned-in address. It may also be known as an Ethernet hardware address (EHA), hardware address or physical address.

MAC addresses are formed according to the rules of one of three numbering name spaces managed by the Institute of Electrical and Electronics Engineers (IEEE): MAC-48, EUI-48, and EUI-64. The IEEE claims trademarks on the names EUI-48 and EUI-64, in which EUI is an acronym for Extended Unique Identifier.

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HFC = Hybrid Fibre-Coax. This abbreviation refers to the port of the cable modem that connects to the CATV coax cable. Some cable ISPs require you to register with them the HFC MAC address of your cable modem.

The HFC MAC address of the cable modem is stamped on the manufacturer's label on the back or underside of the cable modem, or on the label of the box in which the cable modem was sold.

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Cable modems might have multiple MAC addresses, one for the HFC side (cable TV coax socket), and one for the CPE side (Customer Premises Equipment, the ethernet socket). USB-capable cable modems also have two further MAC addresses: one for the cable modem USB socket, and another for the emulated network interface in the USB driver in the PC. Although it is possible to discover the CPE MAC address(es) of the cable modem, there is no application or procedure that requires them.

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I know what does MAC address means. –  Gogoo Jan 10 '11 at 20:31
    
Thats the first part of the question - Media Access Control address (MAC address) is a unique identifier.. –  Kirk Strobeck Apr 7 '11 at 14:56
    
Would you consider accepting this as the answer? –  Kirk Strobeck Apr 7 '11 at 14:56
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Cable modems have multiple MAC addresses.

  • HFC side (Hybrid-fibre connection... the coax cable from the provider)
  • CPE Ethernet (Customer Premises Equipment... standard network socket)
  • CPE USB (Customer side USB connection.. shows up like a USB network card)

Learned are supplied by DOCSIS from the provider over the HFC link.

The SELF address is the HFCs hardware address, used to participate in the DOCSIS assignment from the ISP/Cable company on the coax connection.

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Source

"A modem has two distinct interfaces: the cable interface and the ethernet interface. The HFC MAC is on the cable/DOCSIS side and used to determine what bits are for your modem and which ones are not. The CPE MAC is the same exact thing except on the Ethernet side."

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In analogy form as a general concept:

You can think of an IP address as a cell phone number. It can change but it follows you where ever you go.

You can think of a MAC address as a home address. It is hard coded(though not normally anymore) into the network card as a unique identifier.

So even though you may change your phone number, you can't change your home address. The same is true(loosely) of Mac addresses.

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