The loopback interface is a virtual network interface used basically for two purposes:
- Diagnosis;
- For developing and testing systems that require a network interface with an IP (Webservers, etc).
On a Linux system, type ifconfig to check your loopback interface:
ifconfig
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:65536 Metric:1
RX packets:353933 errors:0 dropped:0 overruns:0 frame:0
TX packets:353933 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:584828381 (584.8 MB) TX bytes:584828381 (584.8 MB)
Because it is a network interface it is possible to stop it:
sudo ifconfig lo down
Just like lifting it:
sudo ifconfig lo up
The diagnostic part can be used, for example, to check if your machine has ssh server active. Try this:
ssh user@localhost
If the machine in question is with an SSH server listening on port 22, then the machine itself will be accessed from it via SSH (see loopback happening). :-)
In the development part of systems, the loopback interface is widely used when you want to develop and run the server (web, tcp, etc.) on the machine itself. Example of an address when developing Java + Tomcat: http://localhost:8080/App or http://127.0.0.1:8080/App
It is interesting to note that the range of Ips associated with this interface is the 127.0.0.0/8
. Therefore, you can drip any of the addresses ranging from 127.0.0.1
until 127.255.255.254
that this interface will answer. However, the most famous is the first, 127.0.0.1
. It is usually in this IP that is associated the famous hostname localhost
.
Who’s to say the guy didn’t screw you up? P
– rray
@rray do not put me in doubt, friend. Actually, after I talked to him: "Is it only working with 0.0.0.0, with localhost not working?" , he made the expression: "Wow, your loopback isn’t running". And then it worked :D
– Wallace Maxters