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The Answer To The Media Access Control Question

Over the past few weeks, I have received quite a few e-mails about Ethernet cards, both wired and wireless, and more specifically, about Media Access Control (MAC) addresses. I think the main reason I’ve received so many questions

about Ethernet cards and MAC addresses is people trying to secure their home wireless networks and their desire to use MAC address filtering. This filtering in wireless networks can be configured to allow or deny specific computers to use or attach to the wireless network, based on the MAC address.

mac

My first thought was to write an article just about MAC addresses and wireless Ethernet. After thinking about it, I decided to expand on this and some specific information about Ethernet cards and communication.

Different Ways Of Finding Your MAC Address And More

There are several ways of finding your Ethernet and communications protocol information. Many Ethernet card manufacturers have proprietary software that can reveal this information, but they work differently depending on the manufacturer. So we will use the Windows 2000 and XP “IP config” utility since this is available in most Windows Operating Systems.

First, go to “start” -> “run” and type “cmd” without the quotes. Then hit the enter key. At the command line, type “config /all” again without the quotes. Actually, typing config without the /all will work but will only provide you with abbreviated information regarding your network cards. An example of what you might see by typing the “IP config /all” command is below, with each item commented in green lettering:

Fault-Tolerant And Highly Availability Computer Systems

There are several ways of finding your Ethernet and communications protocol information. Many Ethernet card manufacturers have proprietary software that can reveal this information, but they work differently depending on the manufacturer. So we will use the Windows 2000 and XP “IP config” utility since this is available in most Windows Operating Systems.

First, go to “start” -> “run” and type “cmd” without the quotes. Then hit the enter key. At the command line, type “IP config /all” again without the quotes. Actually, typing config without the /all will work but will only provide you with abbreviated information regarding your network cards. An example of what you might see by typing the “config /all” command is below:

OutPut Of The “Ipconfig /All” Command

Windows IP Configuration

Host Name . . . . . . . . . . . . : Home Computer

This is the name of your computer, typically defined during the windows installation. However, it can be changed after installation.

Primary Dns Suffix . . . . . . . : domain.com

If your computer participates in a network such as a Microsoft Windows domain, this item may contain the domain’s name.

Node Type . . . . . . . . . . . . : Unknown

The Node Type may say Unknown, or peer-to-peer, or in some cases “hybrid.” It is a setting that has to do with the Windows Internet Naming Services used in certain Windows domain networks.

IP Routing Enabled. . . . . . . . : No

This setting determines if Windows XP or 2000 will function as an IP router. If you have two or more network cards, you can set up your system to act as a router, forwarding communications requests from one network to another. Windows 2000 can be configured to do this pretty straightforwardly; Windows XP will need a registry modification.

WINS Proxy Enabled. . . . . . . . : No

WINS Proxy is another setting that is related to the “Node Type” we discussed earlier. It is normally not required in a home or small office network or newer types of Microsoft Windows domains.

wireless

Ethernet adapter Wireless Network Connection 2:

If you have multiple Ethernet (network) cards on your systems, you will have multiple listings as I do on this laptop. This one happens to be the second Ethernet card, an internal wireless Ethernet card.

Description . . . . . . . . . . . : Broadcom 802.11b/g WLAN

This is the description of the Ethernet card, usually the Name / Manufacturer and type of Ethernet card. In this case, it is a Broadcom wireless Ethernet card built into my laptop.

Physical Address. . . . . . . . . : 00-90-4B-F1-6E-4A

And here we have the MAC address. The MAC address is a 48-bit hexadecimal code and is suppose to be a unique address. It is 48 bits because each number or letter in hexadecimal represents 8 bits. Hexadecimal numbers range from 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E, F. There are 6 alpha-numeric codes hence 6*8=48(bits).

The first 3 codes identify the card manufacturer, and the remaining codes are used to create a unique number. Theoretically, there should never be a card with the same MAC address on a local network. However, there are a few exceptions. There are software tools that allow you to change this code. In fact, this is a step some hackers take to attack other systems on a local network. I say local network because

MAC addresses are not routable between network segments. By spoofing this address, you can impersonate another machine on the local network. Traffic that was bound for the intended target can be redirected to the hacker’s machine. This is the address you would also use to populate a MAC address or physical address table when setting up your wireless access point to support MAC address filtering.

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