When a network connection fails, many network administrators will first use Ping to find the source of the problem. But as long as many people find that Ping is not working, then it is judged that the network is faulty. Judging only by surface phenomena in this way is likely to cover up the truth. So what problems should we pay attention to when using the Ping command? Or please follow me.
1. Request TImed Out
When pinging the specified object, the "Request TImed Out" prompt message appears very frequently, which means that the other party cannot accept the data sent. Of course, in this case, it is likely that the network has failed, but it cannot be determined that the network must be unreachable. Because it may be caused by other reasons.
Host is not online
If the other party shuts down, disables the network card, or unplugs the network cable, no matter how you operate, no connection information will be returned. Know that the simplest is often the most overlooked.
Firewall interception
After the firewall is installed, when the firewall is working, it can generally automatically intercept the Ping command from the network, thereby causing it to lose response. After installing the firewall at the same time, it will also cause the failure of the shared files to be inaccessible. Therefore, you should let the other party turn off the firewall before checking, and then use the Ping command to detect.
IP security policy restrictions
For many experienced network administrators, they have added an IP security policy to the server to filter ICMP messages so that the Ping command cannot respond, thereby returning the "Request TImed Out" error prompt.
Gateway setting error
This situation occurs only when Ping external network address. Because when the gateway is set incorrectly, the data packets sent by Ping cannot be forwarded through the gateway. Therefore, it is necessary to check whether the gateway settings of the machine and the configuration of the remote gateway are correct.
Generally speaking, only after excluding the above reasons, can we preliminarily judge that there may be a problem with the network connection according to "Request TImed Out".
2. Destination Host Unreachable
When the "Destination Host Unreachable" error message appears, it means that the other party's host does not exist or has not established a connection with the other party. It seems similar to "Request Timed Out", but the two are about the essential difference. If the data packet sent by the Ping command passes through the router and reaches the destination route through the routing table, but is unreachable due to other reasons (such as firewall interception, etc.), then it is the prompt of "Request Timed Out"; on the contrary, if If there is no routing information to reach the destination, then "Destination Host Unreachable" will appear.
There are some reasons for this situation: For the network that uses DHCP to automatically assign IP addresses, it is likely that the DHCP server is faulty or not working properly, so that the client cannot communicate with DHCP properly and obtain the correct IP address. You only need to repair the DHCP server; otherwise, the subnet mask may be set incorrectly, and you only need to modify it to the correct one.
3. Unknown host
The prompt indicates an unrecognized host. Does this mean that the target host must be wrong after this problem occurs? Of course not! Because we use the Ping command to connect to the target host name, we mainly use DNS to convert the name into an IP address. For example, "Ping", the return information we see is "Reply from 220.181.28.42: bytes = 32 time = 59ms TTL = 54" instead of "Reply from: bytes = 32 time = 59ms TTL = 54", which means The DNS server in our IP settings will be successfully converted to 220.181.28.42. Therefore, when we see such a prompt, we should check whether the DNS settings are correct and DNS is working properly.
Through the surface phenomena, we can see the real problem clearly. Only in this way can we help us to find the source of the fault, so that we can correctly judge the fault.
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