What do you know about TCP/IP?

Approaching TCP/IP protocol

1. What is TCP/IP?

TCP/IP Protocol (Transmission Control Protocol/Internet Protocol, Transmission Control Protocol/Internet
Is the most basic Internet protocol. Before the formation of the Internet, many small networks have been established around the world, but these networks have different network structures and data transmission rules, they need to be connected to each other, just like for people in different languages to communicate, we need to build a language that everyone can understand, and TCP/IP can achieve this function, it is like the world language on the Internet ".

2. What protocols does TCP/IP contain?

TCP/IP is a set of hundreds of functional protocols. Below are several common ones (see the appendix ).

Eliminate network faults using TCP/IP

Instance 1: plug in the NIC and connect it to the network, but the network is disconnected.

1. Use Ping to determine the fault Scope

(1) Ping 127.0.0.1. If it fails, it indicates that the TCP/IP protocol of the local machine cannot work normally. Please reinstall the TCP/IP protocol and try again.

(2) Ping the local IP address. If it fails, the NIC configuration is incorrect.

(3) Ping the IP addresses of other machines in the LAN or the IP addresses of hosts on the Internet. If the connection fails, the main cause is that the network cable is not connected. If the connection succeeds, but the network is still unavailable, the problem may be caused by the software configuration of the network system.

Tips

If some computers are set to prohibit other computers from performing Ping operations on them in the network firewall, the Ping operation will fail no matter how many times.

2. Eliminate other possible causes of network disconnection

In addition to network settings that may cause network disconnection, there are also other possibilities. The following lists several typical faults:

(1) "Network neighbors" cannot see any computer or access the Internet

Fault description: the IP address of the local machine is successfully pinged, but no other computer is visible in "Network Neighbor" and cannot access the Internet. Check whether the TCP/IP configuration is correct.

Solution:

Most of these problems are caused by computer viruses. They are completely eliminated using the latest anti-virus software.

Reinstall the NIC driver because the driver may have been damaged by viruses.

(2) Some integrated network interfaces cannot access the Internet due to the loss of addresses.

Fault description: the IP address of the local machine is successfully pinged, but the Internet access is not allowed. Run ipconfig to find that the physical address of the NIC is all 00!

Solution: Check the "Integrated Perpherals" (with built-in peripheral devices) in the CMOS settings. In this example, "MAC Address Input" (sets the MAC Address of the NIC) set a value that does not conflict with other network card addresses.

3. Summary

It seems that the reason for network disconnection is nothing more than network installation settings (such as the default gateway, DNS) and other objective factors (such as viruses. When a network failure occurs, you can use Ping, ipconfig, and other related commands, as well as TCP/IP related knowledge such as the nic mac address to analyze and troubleshoot the failure, which often achieves better results.

Example 2: Use the Tracert command to uncover the mysteries of slow network speeds

I often think it is extremely slow to access a website? Do not blame your ISP immediately before you determine the cause, because your computer may have to go through more than 10 network routers before connecting to the website you want to visit, if one or more of these routers are slow, it will become a stumbling block to your quick access to the website. So how can we determine who the stumbling block is?

1. Why is the network speed so slow?

(1) run the Tracert command, for example, run Tracert www.pcpchina.com to view the transmission path of the server you connected to www.pcpchina.com.

(2) view the result (see figure 1), including the response time of each stop and the IP address that stays along the road. If "*" is found on a vro。, it indicates that the data packet is stopped on the vro。, resulting in a particularly slow Internet access speed. However, it may be caused by a router that rejects Tracert requests.

 

2. Tracert failure caused by DNS service problems

Computers on the LAN cannot browse the Internet or send or receive emails externally. Tracert: a domain name immediately fails to be displayed, but the IP address of Tracert is normal. If this problem occurs, it is likely that the domain name resolution server has a problem. You can change the DNS server in the TCP/IP configuration.

Example 3: Access from clients to some websites is abnormal when bandwidth is shared

Nowadays, more and more families are using the "Internet Connection Sharing" provided by Windows to achieve broadband Internet access on multiple computers. Although this method is simple, I believe many of my friends have encountered this problem: the Internet access on the host is normal, but the client cannot access some websites.

Fault Analysis: in Windows, the maximum value of TCP/IP data packets is 1500 by default, while that of ADSL service providers is slightly smaller than 1500, mostly 1492, therefore, reduce the value of MaxMTU to 1492.

Do you know?

Relationship between MaxMTU and network speed

The maximum value of TCP/IP data packets MaxMTU is an important parameter that affects the speed of the Internet. The packet header size is 20 ~ 60 bytes. If you want to send 500 bytes of data, when the MaxMTU value is 1500, you need to send 60 data packets. When the MaxMTU value is, you only need to send 20 data packets, apparently, the former needs to send 40 more headers, totaling 800 ~ 2400 bytes, accounting for 2.6% of the total data volume ~ 7.8%, so when the MaxMTU value is 1500, the speed is improved by about 500 ~ 7.8%. Many ISPs adjust the MaxMTU value to get a faster network speed. The MaxMTU value we set should not be greater than the MaxMTU value of the ISP.

1. Windows 9x/Me

Open Registry Editor and find n items under [HKEY_LOCAL_MACHINE SystemCurrentControlSetServicesClassNetTrans] (This item contains "DriverDesc" with a key value of "TCP/IP "), create a "string" key under "000n" and name it "MaxMTU". Set the key value to 1450 in decimal format, which is generally less than 1492. After the settings are complete, restart the computer.

2. Windows 2000/XP

Go to [HKEY_LOCAL_MACHINE SYSTEMCurrentControlSetServicesTcpipParametersInterfaces] in "Registry Editor", find the item that contains the IP address of your computer, DNS server, default gateway, and other network settings data, and create a double byte value in this item, name it "MTU" and set the value to 1450 in decimal format or a value smaller than 1492. After the settings are complete, restart the computer.

Tips

You can use a dedicated registry optimization tool like Super Rabbit magic settings to modify the MaxMTU value: Enable "use maximum transmission unit" under "network ", change to 1450 or a value smaller than 1492 to restart the computer.

Example 4: identify whether a trojan is in progress through port information

The netstat command can be used to display the port opened during local and external connections and the connection status.

Enter the "netstat-a" command in the "command prompt" and press Enter.

Check the results. If you find information such as Port 12345 (TCP) Netbus and Port 31337 (UDP) Back Orifice, it indicates that the trojan is in use. Hurry up and take the virus!

The future of TCP/IP: IPv6

TCP/IP is a network protocol with both scalability and reliability. With the popularization and rapid development of the Internet, the bottleneck of IPv4 in 4th versions of IP protocol is revealed, its 32-bit addressing function is insufficient to support the number of hosts and networks that need to be added to the Internet. In other words, IP addresses are insufficient. At this time, the new standard IPv6 was born.

Although IPv6 is not yet popular, sometimes IPv6 support is required when a service or software is installed, such as Microsoft's ThreeDegrees software. What should I do? The following describes how to install the IPv6 protocol.

1. Windows 2000

Download the IPv6 package: http://www.microsoft.com/downloads/details.aspx? FamilyId = 27B1E6A6-BBDD-43C9-AF57-DAE19795A088 & displaylang = en.

Decompress the downloaded software to the c: IPv6kit directory.

Right-click "my computer" and select "properties" to view the system's SP version. Different installation methods are available for different versions of Windows 2000.

Windows 2000 SP1: directly execute the setup.exe file under the c: ipv6kitdirectory.

Other versions of Windows 2000 SP:

(1) Run "Start> program> attachment> command prompt", enter the "c: Your 6kitsetup-x" command, and decompress it to the c: Your 6kitipv6 directory.

(2) use NotePad to open the hotfix in the c: IPv6kitIPv6 directory. INI file. In the [VERSION] segment, change NTServicePackVersion = 256 to 512 (applicable to SP2 users), 768 (applicable to SP3 users), or 1024 (applicable to SP4 users) (see figure 2 ).

(3) Run hotfix.exe in the c: ipv6kitipv6directory and click "OK.

(4) After restarting the computer, right-click the "Network Neighbor" icon on the desktop, select "properties", double-click "Local Connection", and select "properties ", click "Install", select "Protocol", click "add", select "Microsoft IPv6 Protocol", and click "OK ".

2. Windows XP

Windows XP: IPv6 protocol has been integrated, so you do not need to download the IPv6 software package. During installation, enter the "IPv6 install" command on the "command prompt" interface to automatically complete the installation.

Windows XP SP1:

(1) Click "Install" in "network connection> Local Connection> Properties ".

(2) In the "select network component type" dialog box, click "protocol> Add → Microsoft TCP/IP Version 6", and then click "OK ".

Tips

★The method for installing IPv6 on Windows Server 2003 is the same as that on Windows XP SP1.

★IPv6 does not support Windows 95/98/Me.

★You can run the "ping6: 1" command to verify whether IPv6 is correctly installed. If yes, the IPv6 protocol has been correctly installed. In fact, this command is similar to ping 127.0.0.1 in IPv4.

As the world's most widely used network protocol, the TCP/IP protocol contains a lot of skills and knowledge. It cannot be elaborated in a book, this article mainly explains some basic knowledge, application skills and related troubleshooting methods, hoping to play a role in attracting others. IPv6 is not very practical at present. It is estimated that it will be useful soon. Let's wait and see!