The answer to the question of media access control
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In recent weeks I have received many emails about network cards, both wired and wireless, and more specifically, about Media Access Control (MAC). I think the main reason why we 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 type of filtering in wireless networks can be configured to allow or deny specific computers to use or connect to the wireless network, according to the MAC address.

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

Different ways of finding your MAC address and More
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There are several ways of finding your Ethernet and communications protocol. Many Ethernet card manufacturers have proprietary software that can reveal this information but they work differently depending on manufacturer. So let's use the Windows 2000 and XP "ipconfig" utility is now available in most Windows operating systems.

First, go to "Start" -> "Run" and type "cmd" without quotes. Then press the Enter key. In the command line type "ipconfig / all" again without quotes. In fact, just typing ipconfig without the / all works, but only provide brief information about the network cards. An example of what can get by typing the command "ipconfig / all" is below each item commented in green letters:

Fault tolerance and high availability of PC systems
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There are several ways of finding your Ethernet and communications protocol. Many Ethernet card manufacturers have proprietary software that can reveal this information but they work differently depending on manufacturer. So let's use the Windows 2000 and XP "ipconfig" utility is now available in most Windows operating systems.

First, go to "Start" -> "Run" and type "cmd" without quotes. Then press the Enter key. In the command line type "ipconfig / all" again without quotes. In fact, just typing ipconfig without the / all works, but only provide brief information about the network cards. An example of what can get by typing the command "ipconfig / all" is as follows:

Output of "ipconfig / all"
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Windows IP Configuration


Host Name. . . . . . . . . . . . : Home Computer
This is the name of your computer, usually defined during installation of Windows. However, it can be changed after installation.

Primary DNS Suffix. . . . . . . : Domain.com
If your team participates in a network as a Microsoft Windows domain this article may contain the domain name.

Node Type. . . . . . . . . . . . : Unknown
The node type can say unknown, or peer-to-peer, or in some cases "hybrid". It's an adjustment that has to do with the service Windows Internet Name used in certain types of Windows domain networks.

IP Routing Enabled. . . . . . . . : No
This value determines whether Windows XP or 2000 functions as an IP router. If you have two or more network cards you can configure the system to act as a router, forwarding communications requests from one network to another. Windows 2000 can be configured to do this in a fairly straight forward, Windows XP requires a registry modification.

WINS Proxy Enabled. . . . . . . . : No
WINS Proxy is another value that is related to the "Node Type" we discussed earlier. Not normally a required parameter in a type of home or small office, or later Microsoft Windows domain.

Ethernet adapter Wireless Network Connection 2:
If you have multiple Ethernet (network) cards in their systems, as I do in this laptop, will have several announcements. This becomes the second Ethernet card, an internal wireless network card.

Description. . . . . . . . . . . : Broadcom 802.11b / g WLAN
This is the description of the Ethernet card, usually the name / manufacturer and type of Ethernet network card. In this case, it is an integrated Ethernet Broadcom wireless card on my laptop.

Physical Address. . . . . . . . . : 00-90-4B-F1-6E-4A
And here is the MAC address. The MAC address is a 48-bit hexadecimal code and is supposed to be a totally unique. It is 48 bits, since each number or letter in hexadecimal represents 8 bits. Hexadecimal numbers go 0,1,2,3,4,5,6,7,8,9, A, B, C, D, E, F. There are 6 alphanumeric codes so 6 * 8 = 48 (bits). The first 3 codes identify the manufacturer of the card and the remaining codes are used to create a unique number. In theory there should never be a card with the same MAC address on a local network. However, there are some exceptions. There are software tools that let you 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. For falsification of this address, you can impersonate another machine on the network. Traffic heading for its target can be redirected to the hacker's machine. This is the address which is also used to populate a MAC address or physical address table when setting up your wireless access point to support MAC address filtering.

DHCP enabled. . . . . . . . . . . : Yes
DHCP, or protocol dynamic host control, if enabled means your IP address of your PC is being provided by a DHCP server on your network. The DHCP server can be your wireless access point, router, Cable / DSL, cable modem, or a server on the network. Also, if a DHCP server is not enabled on your network, your computers operating system will automatically generate a random IP address within a certain predefined range. This means that you can network a group of systems together without having to manually assign the IP settings.

IP Address. . . . . . . . . . . . : 192.168.0.117
This parameter gives you your current IP address. The above address is what is called a "private" address. There are certain classes of IP addresses that are reserved for private use. This means for the internal network, local or private home or office. These addresses are not or may not be routed over the Internet. Internet routes what are called "valid" IP addresses. Your cable / DSL or cable modem has an IP address assigned to interface "outside" of the network. The external interface may be your phone line or cable TV cable.

Subnet Mask. . . . . . . . . . . : 255.255.255.0
The subnet mask is a special number, or in some sense, the filter, which breaks your IP address, in this case the private IP address, in certain groups. IP addresses and subnet masks can be a complicated issue and it would take an article for review.

Default Gateway. . . . . . . . . : 192.168.0.254
The default gateway, IP addresses listed above, is the IP address of the device that will route your request, for example, when you try to browse a website, the Internet. It's a bit more complicated than that, though as gateways or routers can route traffic to several different networks, including private networks. In your home or small office, this gateway is likely that the cable / DSL modem or router.

DHCP Server. . . . . . . . . . . : 192.168.0.49
The DHCP server, I remember we talked a little about this before, is the device that assigns your computer an IP address and other information. DHCP servers can assign all kinds of information, such as default gateway, domain name server (DNS), IP address, subnet mask, time server, and more.

DNS servers. . . . . . . . . . . : 192.168.0.49, 64.105.197.58
DNS servers are internal or external servers to resolve domain names (FQDN) as www.defendingthenet.com to IP addresses. This is because computers do not actually transmit their requests with the domain name, you use the IP address assigned to FQDN. For most home or small office users, the DNS server is the IP address of your cable / dsl router. Your cable / dsl router that outpatient Internet DNS server to perform the actual resolution of the FQDN of the IP address. The address 192.168.0.49 is a private internal device on my network, while the external 64.105.197.58 Internet is a DNS server, and is present only in the case of my router has trouble doing the work of DNS resolution.

Grant obtained. . . . . . . . . . : Sunday, March 19, 2006 6:38:16 PM
This information tells you when your computer receives its IP address and other information from a DHCP server. You will notice that says "Lease Obtained", that is because most DHCP servers only lease the IP address that a group of addresses. For example, your pool may be 192.168.1.1 through 192. 168.1.50. So your DHCP server has 50 IP addresses to choose from when assigning your computer's IP address.

Lease Expires. . . . . . . . . . : Wednesday, March 29, 2006 9:38:16 PM
When the IP address assigned by the DHCP lease expires we will try to lease the same or another IP address. This function usually can be changed at the DHCP server. For example, in some fully functional DHCP server, you can set the lease to never expire, or at the expiration of 1 day and so on.

Why MAC addresses so important and how
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To jump back to the MAC address of a bit. You may think that IP addresses are the most important thing when it comes to network communication. The reality is that MAC addresses are very important because without them computers would not be able to communicate over Ethernet networks. When a team wants to talk to another computer on a local network, there will be a broadcast request, or ask a question of who owns a particular IP address. For example, the team can say, "Who is 192.168.0.254." With this information, my default gateway is 192.168.0.254 and answer "I am" 00-90-4B-F1-6E-4A "192.168.0.254". That sends its MAC address. That MAC address then enters what is called Address Resolution Protocol (ARP) on your computer. You can view this information, go to command prompt, as it did above and typing "arp-a". You will receive information such as:


Internet address type physical address
192.168.0.49 00-12-17-5c-a2-27 dynamic
192.168.0.109 00-12-17-5c-a2-27 dynamic
192.168.0.112 00-0c-76-93-94-b2 dynamic
192.168.0.254 00-0E-2E-2E-15-61 dynamic

How a hacker can use MAC addresses in an attack
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You'll find the right IP addresses and MAC addresses them. Without this information, without the MAC address, you will not be reading this article now. MAC addresses are not routable IP addresses. They work in local or private network. However, Internet devices perform the same tasks. Routers and switches maintain a list of your devices MAC address pairs as their computers and network devices in your home or office. I mentioned earlier that MAC addresses can be changed to redirect requests. For example, if I were in your office network, and has an internal web server that was personal information as input, I noticed your team to go to my laptop to the site by spreading my MAC address tied to the real web server IP address. I would do this when your computer asks, "Who is the" Real Web Server "". I can set up a fake web server that looks like the real thing, and start collecting information the real web server normally collected. You can see how dangerous it can be.

Conclusion
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There are several other easy ways you can find your MAC address but can be a little confusing if you have more than one internal network card. More external USB, PCMCIA or cable and wireless Ethernet cards have MAC address printed on them. In cases where the card is wired or wireless network within your team, such as laptops, the MAC address is sometimes printed on the bottom of the notebook. Even cards desktop systems that are inserted into the PCI slot has the MAC address printed on the Ethernet card.