Loopback address also called localhost is a reserved IP address. If we send packets to this IP address it will be rerouted to the computer itself. So loopback address is used to troubleshoot TCP/IP related issues on a PC. This article explains a rare situation where you cannot ping any IP address including the DNS server but can successfully ping loopback address. Before explaining this issue, I would like to explain the concept of loopback. The IP address in the range 127.0.0.1 - 127.255.255.255 are private and can be used as loopback but we normally use 127.0.0.1 as the loopback or localhost. Now let us check the scenario where you can successfully ping 127.0.0.1 but not any other external IP.
Here I ping 4.2.2.2 from the command prompt but it failed to get a valid reply from it. However, when I ping 127.0.0.1, I am getting valid replies. Possible reasons from no valid reply from DSS server though I get replies from loopback address are:
If you are getting a reply from the loopback address it shows the TCP/IP suite is working on your computer. However, it is important to verify it by sending ping packets to 127.0.0.1 and analyze the reply.
After verifying the status of the TCP/IP suite, we must check the network connection. Here we must make sure there is no loose connection or faulty cable. Verify the Ethernet cable connected properly between your LAN port and Modem/router. Also, verify the quality of Ethernet cable. To get more inputs about this issue, I suggest you visit the link below.
How to check my Local Network Connection issues
If you are getting valid replies from localhost, next you must ping any DNS address. You may go through the instructions provided in the link below to learn more about it.
I Am Getting Replies From DNS Server
Explanation
Here I ping 4.2.2.2 from the command prompt but it failed to get a valid reply from it. However, when I ping 127.0.0.1, I am getting valid replies. Possible reasons from no valid reply from DSS server though I get replies from loopback address are:
- The TCP suit on your computer might be corrupted
- Connection Issues in the network
- There is no internet connection from your service provider.
If you are getting a reply from the loopback address it shows the TCP/IP suite is working on your computer. However, it is important to verify it by sending ping packets to 127.0.0.1 and analyze the reply.
- Click on start
- Click on run and type cmd on it then click OK(On Vista type command on search and press enter)
- Ping Loopback
On the command prompt type, the following command ping 127.0.0.1 and press enter key. If you are getting replies, then the TCP/IP suite is fine. If not, you must reset the TCP/IP suit on your computer. To learn how to do it, I recommend you to visit the link below.
There is No Reply From Loopback
After verifying the status of the TCP/IP suite, we must check the network connection. Here we must make sure there is no loose connection or faulty cable. Verify the Ethernet cable connected properly between your LAN port and Modem/router. Also, verify the quality of Ethernet cable. To get more inputs about this issue, I suggest you visit the link below.
How to check my Local Network Connection issues
If you are getting valid replies from localhost, next you must ping any DNS address. You may go through the instructions provided in the link below to learn more about it.
I Am Getting Replies From DNS Server
