# Loopback ping ?



## reezin14 (Oct 16, 2007)

I was wondering what can a loopback ping(127.0.0.1) be use for.I've read that this can be used even if a nic card isn't installed,so what's the point of this command ? I thought it could be use to tell you if your nic is working correctly or not.TIA


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## Courtneyc (Dec 7, 2003)

The loopback ping does not test your network card; it tests the TCP/IP protocol.

Courtney


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## reezin14 (Oct 16, 2007)

Could you explain more please.


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## Courtneyc (Dec 7, 2003)

In order to access the Internet, you need three things: a client, an interface, and a protocol. 

The client is called "Client for Microsoft Networks." This is the default.

The interface is the network card, whether it be a network interface card, a wireless radio, an IEEE 1394 (FireWire) port, or a USB port with an adapter.

The protocol is a set of rules that everyone who wants to communicate with each other, must follow. The agreed upon protocol for the Internet is a suite of protocols commonly called Transmission Control Protocol / Internet Protocol (TCP/IP). Although some people believe that there are only two protocols involved, there are actually quite a few. There are week-long classes on the subject. (I know, I am an instructor.)

The loopback address 127.0.0.1 is identified by Windows (or whatever operating system you use) as a loopback address. In fact 127 anything is a loopback address. If you were to ping 127.34.2.87, it would still come back as a loopback.

If you were to study the TCP/IP protocol, you would eventually encounter the OSI model, which consists of layers. To send packets to the Internet, you go down the layers to layer 1 before it gets out onto the wire.

The network card operates at layers 1 and 2. To test TCP/IP, you only have to go down to layer 3. Pinging the loopback address goes down to layer 2, but it doesn't actually send anything out.

If you wanted to test the network card, you would ping the actual address of the network card, then the default gateway. This would tell you that your network card is working and that you are able to route traffic.

You can see all this by going to a command prompt and typing "route print." If you have just one network card, you will still see two interfaces. One will be your IP address; the other will be the loopback address.

Courtney


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