MAC = Medium Access Control.
MAC addresses are used as the source and destination addresses for data packets on a LAN. A MAC address is written as 12 hexadecimal characters (0-9, A-F). The grouping of those 12 characters into pairs separated by colons (00:20:40:70:F4:84) or hyphens (00-20-40-70-F4-84) is purely conventional, and is not related to function. Every network device in the world has a unique MAC address. The first 6 characters of the MAC address are unique to the manufacturer of the device. Allocation of MAC addresses is administered by the IEEE in the USA.
For some of the procedures described elsewhere on this site it is necessary for the user to discover various MAC addresses: the instructions for finding the following MAC addresses are listed on this page:
Each network interface in your PC will have a different MAC address. Some cable ISPs require you to register with them the MAC address of the network interface of the PC/device that is connected to the cable modem. To discover the MAC address of a PC network interface, proceed as follows.
2 Ethernet adapter : Description . . . . . . . . : Intel DC21041 PCI Ethernet Adapter Physical Address. . . . . . : 00-60-1D-F6-7E-5C DHCP Enabled. . . . . . . . : Yes IP Address. . . . . . . . . : 184.108.40.206 Subnet Mask . . . . . . . . : 255.255.255.0 Default Gateway . . . . . . : 220.127.116.11 DHCP Server . . . . . . . . : 18.104.22.168 Primary WINS Server . . . . : Secondary WINS Server . . . : Lease Obtained. . . . . . . : 07 26 01 21:22:01 Lease Expires . . . . . . . :
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.
|Cable Modem model||Identifying label||Typical address range|
|Motorola Surfboard 3100||HFC MAC ID:||00:20:40:xx:xx:xx|
|Motorola Surfboard 4100||HFC MAC ID:||00:20:40:xx:xx:xx
|Terayon TeraJet||MAC Addr||00:E0:6F:xx:xx:xx|
|Pace digital STB||00:50:94:xx:xx:xx|
|ntl:home 100/120 (Ambit)||under barcode||00:D0:59:xx.xx.xx|
It is not possible to discover the HFC MAC address of the cable modem by use of any commands such as winipcfg or ipconfig on the PC. However, if the cable modem offers diagnostics via a web page, the HFC MAC address might be listed there.
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.
This procedure only works for PCs/devices in the same same IP sub-net as the PC doing the discovery.
For Apple Mac OS 8.x/9.x, the utility IPNetTuner can display the ARP cache of MAC addresses.
For Apple Mac OS X:
If you have a NAT router between your PC(s) and the cable modem, and if your cable ISP normally requires you to register the MAC address of your PC's network card, then you will instead need to register the MAC address of the WAN port of your NAT router.
To discover the MAC address of the WAN port of your router, please consult the documentation for your router. For instance, the procedure for the Linksys BEFSR41 is:
If you want to insert a NAT router between your PC and the cable modem, you might want to avoid changing the client MAC address that the cable modem connects to, for either of these reasons:
Many NAT routers intended for the domestic market have the ability to clone the PC's MAC address into the MAC address of the WAN port. For best effect, you should do the cloning before you first connect the router to the cable modem. To discover how to clone, please consult the documentation for your router. For instance, the procedure for the Linksys BEFSR41 is:
If the router had already been connected to a cable modem, then after cloning a new MAC address into the WAN port, you must perform the procedures of Swapping computers on the cable modem.
With the cloned MAC address in the router's WAN port, then as far as the cable modem is concerned, it is talking to the original PC.
Return to Index.