Further, some commands such as ping mpls require a loopback address to function correctly. You can apply stateless firewall filters to the loopback address to filter packets originating from, or destined for, the Routing Engine. Junos OS creates the loopback interface for the internal routing instance, which prevents any filter on lo0.
Understanding Interfaces. Help us improve your experience. Let us know what you think. Active 1 year, 2 months ago. Viewed 65k times. Improve this question. Only social intertia avoids us to use all Add a comment. Active Oldest Votes. Improve this answer. Slartibartfast Slartibartfast 3, 16 16 silver badges 16 16 bronze badges. I can attest to have found 1 useful in something I'm currently working on where I make other private servers appear to be on localhost via SSH tunneling.
But this is not the case in IPv6? IPv6 has link-local addressing. Not the same thing, but applicable. SuperUser reader Roee Adler, curious about the default localhost IP, posed the following question to the community:. What is the meaning, indeed? John T writes:. But using any other numbers for the host portion should work fine and revert to using You can try it yourself by pinging Why they waited until the last network number to implement this? For example, the address 0. Even as early as September RFC , 0 and were already reserved:.
It might have made more sense to choose 1. While we all know and love Have something to add to the explanation? Sound off in the the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion threads here.
Browse All iPhone Articles Browse All Mac Articles Do I need one? Browse All Android Articles Browse All Smart Home Articles The term loopback sometimes spelled loop-back is generally used to describe methods or procedures of routing electronic signals, digital data streams, or other flows of items, from their originating facility quickly back to the same source entity without intentional processing or modification.
This is primarily intended as a means of testing the transmission or transportation infrastructure. In terms of IP addresses this means that any communications to that address effectively never leave or perhaps never actually enter your network interface card so that you always have a "connection".
A loopback address is "connected" to a virtual network card in your machine called the loopback adapter. Anything sent to the virtual loopback adapter comes right back out of it. It's like it's "connected to itself. So, if you have web server running on your system, and it's listening on Nothing going through the loopback adapter goes out to the Internet, or leaves your system. The loopback adapter is completely contained within your system.
It simply means your local address. When you test your NIC, this can be done via "ping When you do this you are testing to make sure that your information can go down to layer 1 and back up. If you suspect that your NIC is not working on a physical level, this makes a very good test. It can also be used to specify to your applications that you do not want your information to leave the host computer.
This can be seen when you have a server-client model application installed on the local computer, but you do not want that information to be accessible remotely. You can specify the server software to transfer information via the loopback address and your client software could listen in on the loop back address. This would provide the information to local applications, while disabling the ability for somebody else on a LAN to access whatever server software you set up as local.
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