Loop-back/loopback)

From: http://blog.csdn.net/ljinddlj/article/details/5935520

The loopback interface is a virtual network interface, which has different meanings in different fields.

 

1.TCP/IPLoopback interface in protocol stack

 

In TCP/IP, the loopback device is a virtual network interface implemented by software, which is not associated with any hardware. Loopback interfaces are generally integrated into the internal network framework of computer systems.

 

Loopback address in IP protocol

Rfc2606 clearly states that the standard Domain Name of the loopback address is localhost. In IPv4, the corresponding IP address is always 127.0.0.1; in theory, the entire region IP segment (127.0.0.0 ~ 127.255.255.255. In IPv6, the IP address of localhost is 0: 0: 0: 0: 0: 0: 0: 0: 1.

 

Loopback interface functions

1. Used for network service testing to avoid security issues arising from remote network access;

Generally used as a network service test for the client/server type. During the test, the client and server run on the same host, and the client accesses the server by using the loopback address. The most common example is Web service testing. Generally, we use http: // 127.0.0.1/or http: // localhost/to access the local web service.

 

2. Test the IP protocol stack

Ping the loopback address to test whether the IP protocol stack in the operating system is normal.

 

3. In the network, all data packets whose source address belongs to the loopback address will be discarded.

The IP protocol stipulates that loopback packets cannot be transmitted over the network. The network interface must discard the received loopback packet.

 

2.In the network deviceLoopback

In a network device, loopback is used to represent some virtual interfaces used for management purposes. Its meaning does not mean "loopback.

 

The loopback Virtual Interface is assigned an IP address, but this IP address does not correspond to the actual physical interface. Loopback addresses in network devices are mainly used for management purposes, such as alarms issued by devices. Applications (administrative programs) in network devices use the loopback address to send data streams that can receive data, rather than the address of the actual physical interface. For external users, you can directly use the loopback address to view the corresponding information (such as alarm information) of the device, regardless of the physical address of the network card.

 

Here we can also regard this address as the address of a service provided by a network device.

 

3.Communication inLoopback

In the communication field, loopback is a testing method that directly returns received signals or data to the sender through software or hardware. As a test method, many communication devices can configure the port data transmission mode (such as the All ones mode) to detect signal reception on the same port. This test is also called "loop test ".

 

Hardware loopback

It generally refers to physically connecting the sending and receiving channels. In this way, all data packets sent through the loopback device will be received by themselves. Generally, this physical loop device is used to test the circuit connection between two points at different positions. For example, a test signal is sent at one end, then, the connection status of each phase is tested by using the return signal method returned by the loop device at different locations.

 

Refer
Http://en.wikipedia.org/wiki/Loopback