英国留学生作业：Ping命令在网络维护中的用途
As the administrator of a school computer room, I think the network maintenance process ping command is the first one must master the DOS command, which is used to check whether the network or the network connection speed smooth command. Using the principle is this: the use of the machine on the network IP address is unique to the destination IP address to send a data packet, and then ask to return a similarly sized data packets to determine whether the machine is connected to two network connected, delay how much. It is built on the Windows system TCP / IP protocol, the need for a separate installation. Ping command is powerful, it can detect the connectivity between networks, or the detection of network transmission instability.
作为作为学校微机室的管理员，我觉得在网络的维护过程中ping命令是第一个必须掌握的DOS命令，它是用来检查网络是否通畅或者网络连接速度的命令。它所利用的原理是这样的：利用网络上机器IP地址的唯一性，给目标IP地址发送一个数据包，再要求对方返回一个同样大小的数据包来确定两台网络机器是否连接相通，时延是多少。它内置于Windows系统的TCP/IP协议中，无需单独安装。Ping命令功能强大，通过它可以检测网络之间的连通性，或检测网络传输的不稳定性。
1 Use the ping command to test network card and its configuration
1.利用ping命令测试网卡及其配置
Ping the computer by using the local IP address or ping127.0.0.1 can be directly installed correctly detect whether the computer LAN equipment, network equipment is installed TGP / IP protocols, and network card is properly configured with an IP address and subnet mask. Specific forms of use are: ping local IP address or ping127.0.0.1. If the local IP address to ping the computer successfully, the following message is displayed
通过使用ping计算机的本地IP地址或ping127.0.0.1可直接检测计算机是否正确安装了网卡设备，网卡设备是否安装了TGP/IP协议，以及网卡是否正确配置了IP地址和子网掩码。具体使用形式是:ping本地IP地址或ping127.0.0.1。如果ping计算机本地IP地址成功，则会显示如下信息
Replay from 172.168.200.2 bytes = 32 time <10ms
Ping statistics for 172.168.200.2
Packets Sent = 4 Received = 4 Lost = 0 0% loss
Approximate round trip times in milli-seconds
Minimum = 0ms Maxiumu = 1ms Average = 0ms
Description NIC device TCP / IP protocol has been installed correctly. If in MS-DOS mode, run this command to display the contents: Request timed out, it indicates that the NIC installation or configuration problem. Disconnect the network cable to run this command again, if the display is normal, then the IP address of the machine may be used with another IP address of the machine being used to repeat. If it still is not normal, it indicates that the local network card installation or configuration problems, need to continue to check the relevant network configuration. On the contrary, indicating that the network card driver is correct, may not be installed TCP / IP protocol. Here is the card comes with default 127.0.0.1 IP address, regardless of whether the card assigned an IP address, which will continue to exist, and is valid on the local computer in the network is invalid.
2.Ping gateway IP
Gateway IP is assumed: 172.168.6.1, then execute the command Ping 172.168.6.1. In MS-DOS mode, run this command, if the display similar to the following information:
Reply from 172.168.6.1 bytes = 32 time = 9ms TTL = 255 http://www.ukthesis.org/jsjwl/
Ping statistics for 172.168.6.1
Packets Sent = 4 Received = 4 Lost = 0
Approximate round trip times in milli-seconds
Minimum = 1ms Maximum = 9ms Average = 5ms
It indicates that the LAN gateway router is operating normally. Not vice versa, then the gateway problem.
3.Ping remote IP
This command can detect whether the machine properly access the Internet. Such as the local telecom operator's IP address: 202.102.48.141. In MS-DOS mode, execute the command: Ping 202.102.48.141, if the screen displays:
Reply from 202.102.48.141 bytes = 32 time = 33ms TTL = 252
Reply from 202.102.48.141 bytes = 32 time = 21ms TTL = 252
Reply from 202.102.48.141 bytes = 32 time = 5ms TTL = 252
Reply from 202.102.48.141 bytes = 32 time = 6ms TTL = 252
Ping statistics for 202.102.48.141
Packets Sent = 4 Received = 4 Lost = 0 0% loss
Approximate round trip times in milli-seconds
Minimum = 5ms Maximum = 33ms Average = 16ms
Indicates normal operation, the normal Internet access.
On the contrary, it indicates that the host file (windows / host) problems.
4 LAN connection using the ping test
In the LAN connection between computers Unicom situation LAN via ping other computers or server name or IP address of the computer you can test the same network (or VLAN) is properly connected. Specifically the following cases:
(A) detect the IP address and subnet mask settings are correct
By ping LAN computer name or IP address, if not pmg pass, should proceed to check the machine's IP address and subnet mask settings are correct, check the IP address is set to the same subnet IP address, subnet mask code setting reasonable and consistent.
(2) detect the network connection is correct
If the LAN computer's IP address and subnet mask is set correctly, use the ping command to ping the local area computer name or IP address is still not successful, the game should proceed within the network devices such as switches or Hub and communication transmission media - cable, connector other piecewise inspection, testing and troubleshooting.
5.ping command common error message
(1) Request timed out
a. the other side has been shut down, or did not have the address on the network: for example, in the figure above in host A PING 192.168.0.7, or shut down the host B, host A in PING 192.168.0.5 will get the information out.
b. each other and they're not the same network segment, by routing can not find each other, but sometimes the other does exist, of course, there is also a return timeout message.
c. other side does exist, but the set up ICMP packet filtering (eg firewall settings)
How do you know each other exists, or does not exist, it can be used with the Ping command parameter-a probing each other, if we can get each other's NETBIOS name, the other party is there, there is a firewall settings, if not, mostly they do not exist or is shut down, or not in the same network segment. d. Errors set the IP address
Under normal circumstances, a host should have an adapter, an IP address, or multiple network cards, multiple IP addresses (these addresses must be in different IP subnets). However, if a computer "Dial-Up Networking Adapter" (equivalent to a soft NIC)'s TCP / IP settings, set up a LAN IP address in the same subnet as the IP address, so it seems at the IP layer protocol, which hosts have two different interfaces on the same network segment. When this host Ping other machines when there is a problem:
A. I do not know the host to which the packet is sent network interface, because there are two network interfaces are connected to the same network segment.
B. host does not know which address as the source address of the packet. Therefore, from this host to Ping other machines, IP layer protocol will not be processed after the timeout, Ping will give a "no answer timeout" error message alert. But other hosts Ping this host, the request packet from a specific network card, ICMP simply enter destination, source address interchangeable and can change some signs, ICMP response packet can successfully issued, other hosts will also be able Ping successfully pass this machine.
(2) Destination host Unreachable
Each other and they're not the same network segment, while he has not set the default route, such as the example machine A default route is not set, run the Ping 192.168.1.4 appears "Destination host Unreachable".
Network cable out of the failure
Here to explain "destination host unreachable" and "time out" the difference, if the routers in the routing table has a route to reach the target, and the target can not be reached because of other reasons, this time there will be "time out", if even reach the target routing table routing are not, then there will be "destination host unreachable".
(3) Bad IP address
This message indicates that you may not be connected to the DNS server, so it can not resolve the IP address, or it may be an IP address does not exist.
(4) Source quench received
This information is rather special, it appears very little chance. It means that the other party or the middle of a busy server can not respond.
(5) Unknown host - unknown host
This error message means that the remote host's name can not be domain name server (DNS) into IP addresses. Failure may be due to a faulty name server, or the name is incorrect, or the network administrator's system and the lines of communication between the remote host has failed.
(6) No answer - no response
This failure indicates that the local system has a route leading to the central host, but can not receive it on to the central host any of the information. Failure may be due to one of the following: central host did not work; local or central host network configuration is incorrect; local or central router does not work; communication line is faulty; central host routing problems exist.
Tips:
In order to effectively identify network failure reason we use the Ping command to test check, try to make sure the LAN is configured with only one gateway, while ensuring local workstation IP Security Policy is not enabled, so you can ensure the Ping command to obtain the correct test results.
