MAC address cloning and cracking sharing restrictions allow multiple computers to access the Internet

Author:Laocai

At present, ISPs in many places use the MAC function, that is, to record the MAC address of a machine in your LAN to restrict the sharing of multiple computers. What is a MAC address? How can I cope with MAC Internet access restrictions?

1. Learn about MAC addresses

Network devices (including various wired and wireless NICs, broadband MODEM, and broadband routers) use two types of addresses: IP addresses and MAC addresses. The MAC (Media Access Control) address is the physical address of the network device. It identifies a LAN computer.

The length is 48-bit binary, from 12 00 ~ 0FFH consists of hexadecimal numbers. Each hexadecimal number is separated by ":". For example, the MAC address of a network device is "08: 00: 20: 0A: 8D: 6E ", where the first six hexadecimal digits 08:00:20 represents the number of the network hardware manufacturer, which is allocated by the IEEE (Association of Electrical and Electronics Engineers), and the last three hexadecimal digits 0A: 8D: 6E indicates the number of a network product (such as a NIC) manufactured by the manufacturer.

Both the IP address and MAC address are in binary format on the computer. The IP address is 32 bits, while the MAC address is 48 bits. IEEE divides Ethernet addresses into several independent continuous address groups. manufacturers that produce Ethernet network devices purchase one of them. During actual production, the physical address is usually the EPROM that is burned into the NIC by the NIC manufacturer (a flash memory chip that can be erased by a program ), this allows you to identify the address of the computer that sends data and the host that receives data when transmitting data like an "ID card.

Just as the MAC address is the only identifier of the network device like our ID card, the broadband access provider can block more access computers in the family based on the MAC address.

To know the MAC address of the local Nic, choose Start> RUN> enter winipcfg> press enter in Windows 98/Me, the MAC address is displayed. in Windows 2000/XP, choose Start> RUN> CMD> press enter> ipconfig/all> enter, you can also find the MAC address.

Ii. How to restrict MAC addresses

The IP address is like a car, And the MAC address is like a driver's license required to operate the car. If you have a driver's license, you can drive the car, but you must have a valid driver's license, otherwise, you will be fined or banned from driving. That is to say, there is no bound relationship between the IP address and the MAC address. The packet movement between nodes in the network is completed by ARP (Address Resolution Protocol: Address Resolution Protocol) which maps IP addresses to MAC addresses, therefore, if you want to accurately find the desired "Site" on the mobile phone, a fixed MAC address is required.

This is precisely because the MAC address is the only identifier of the network device. This uniqueness just benefits network management. By bundling IP addresses and MAC addresses, the ISP, it can easily prevent IP address theft or Internet sharing in the LAN and prevent unauthorized access.

Most vrouters or network management switches have such functions and support binding IP addresses and MAC addresses. Management personnel can control users' access to the international Internet based on IP addresses, ports, and MAC addresses, prevents unauthorized users from accessing wired or wireless networks and IP spoofing attacks. For dynamic IP addresses, create a DHCPhtml "target = _ blank> server to bind the MAC address and IP address of the user's Nic, and then set permissions based on different IP addresses.

For vrouters or network management switches, you can use the MAC address filtering policy to achieve this goal. Click "Import address" to import the MAC addresses and IP addresses of all computers on the main program interface. If the policy of a MAC address is pass, the MAC address is allowed to pass. If the policy of a MAC address is blocked, the MAC address is forbidden to pass. If "Address binding" is selected, You can bind the MAC address to the IP address. After the address is bound, the MAC address can only use the specified IP address, if it is changed to another IP address, it cannot be passed.

For static IP addresses, if a layer-3 switch is used, you can limit the IP address and MAC address on each port of the switch. The method is to match the junction box on the user wall with the port of the switch one by one during cabling, and then fill in the collected MAC address with the corresponding switch port, and then bind it with the IP address, reach the three bindings of the IP-MAC-PORT (port. In this way, if you change the IP address and MAC address of a client or the IP address and MAC address of another client, the PC or other computer cannot connect to the network.

In practice, for many broadband networks connected through LAN, the installer can easily bind the IP address and MAC address to restrict multi-host sharing.

Assume that the IP address assigned by a computer is 192.168.1.112 and the MAC address is 00-20-6C-DD-73-B4. Open the MS-DOS window in Windows 98, in Windows 2000/XP, click Start → run → Enter CMD → press Enter. In the MS-DOS mode or Command Prompt window, enter the command (for example): ARP-s 192.168.1.112 00-20-6C-DD-73-B4 to bind the MAC address and IP address. If a network device or computer using another MAC address wants to access the Internet, it will be rejected and cannot access the Internet normally.

Iii. How to break through MAC restrictions

Binding MAC addresses and IP addresses is a common, simple, and effective measure for network administrators or operators to prevent IP address theft. However, for many home users, the utilization rate and ease of use of multi-host broadband are greatly reduced. In general, the following methods can be used to break through such restrictions (if any:

① Modify the MAC address of the NIC

The MAC address is stored in the ENI's EEPROM and uniquely identified. However, when the NIC Driver sends an Ethernet packet, it does not read the MAC address from the EEPROM, but creates a cache area in the memory, the source MAC address of the Ethernet packet. In addition, you can modify the source MAC address in the actually sent Ethernet packet through the system style = "COLOR: #000000" href = "http://product.it168.com/list/ B /0501_1.shtml" target = _ blank> operating system.

Open the "Network Neighbor" attribute, select the corresponding network adapter and select the attribute, and click "Configure" on the "General" page of the property page. On the configuration properties page, select "advanced", select "Network Address" in the "properties" column, and select the input box in the "value" column, then, in the enter box, the user can access the MAC address of the computer normally and set it to the same IP address. However, this method is only applicable when a computer needs Temporary Internet access.

② Share the Internet with the host

ARP commands are only useful for LAN proxy servers and for static IP addresses. If MODEM is used for dial-up or dynamic IP addresses, therefore, you can use gateway software such as ICS to achieve multi-host sharing.

The implementation method is described several times before. The host uses MODEM dial-up Internet access. The host IP address is set to 192.168.0.1, the Client IP address is 192.168.0.2, and the default gateway is 192.168.0.1. Then enable connection sharing on the host. This method can also achieve multi-host access through a switch, but the disadvantage is also obvious, it must occupy a host as a server