The loopback device is a special, virtual network interface that your computer uses to communicate with itself. It is used mainly for diagnostics and troubleshooting, and to connect to servers running on the local machine. When a network interface is disconnected--for example, when an Ethernet port is unplugged or Wi-Fi is turned off or not associated with an access point --no communication on that interface is possible, not even communication between your computer and itself.
The loopback interface does not represent any actual hardware, but exists so applications running on your computer can always connect to servers on the same machine. This is important for troubleshooting it can be compared to looking in a mirror.
The loopback device is sometimes explained as purely a diagnostic tool. But it is also helpful when a server offering a resource you need is running on your own machine. For example, if you run a web server, you have all your web documents and could examine them file by file.
You may be able to load the files in your browser too, though with server-side active content, it won't work the way it does when someone accesses it normally. So if you want to experience the same site others do, the best course is usually to connect to your own server. The loopback interface facilitates that. For IPv4 , the loopback interface is assigned all the IPs in the That is, For most purposes, though, it is only necessary to use one IP address, and that is This IP has the hostname of localhost mapped to it.
Like other network adapters, the loopback device shows up in the output of ifconfig. Its name is lo. One common, production i. In a web browser, go to:. All the If you come from a Windows background, you might expect loopback to itself be a synonym of localhost and thus to be able to ping loopback , connect to servers on loopback , and so forth.
That behavior is peculiar to Windows. The general concept of loopback is a mechanism through which a message or signal ends up or loops back to where it started.
So there are a few other ways loopback is use in Ubuntu that should not be confused with the loopback device in networking. This is usually called a loop device and not a loopback device , but the term loopback file interface is occasionally used.
Pulseaudio's loopback module facilitates this. Here, it is correct to use the term loopback , but like loop mounts, this also has nothing to do with the loopback device in networking. And nothing to do with loop mounts, either.
I'm little bit confused about this loop back addresses. We had this question many times before. It is also worth using the search facility of CLN. Hey all Thanks for the reply I'm new here so i dont know much about the site.. Vlan interfaces are generally used for management on switches and Loop-backs are often used for management on routers.
That's the primary difference. It has long been recommended that a loop-back address be used for management on routers. The thinking behind that is that if there is any way to your router you can get to the loop-back - if you used a real interface address if that was the interface that was down, you would lose access. The main reason for using a loop-back on a switch as the management address is that it would fall in line with a simple policy "we always use lo0 as management, lo1 - 9 as tunnel end points" sort of thing, and there is no need to modify the policy for routers or switches, and standard security configs may be a little easier.
Unlike a physical interface, the loopback interface never goes down and hence has many uses. In BGP it is used to establish peering between neighbors, so that if even if the physical interface went down for a short time the session does not go down and we can use any network address on the loopback interface. If the loopback address is included in the routing process, the route gets advertised.
Choose the address carefully. Use an address that is not used elsewhere on your network. Some engineers used the loopback for managing routers and reserve a network segment for the loopbacks. For example, router 1 has the loopback Loopback interfaces will only go down, if explicitely set to shutdown, otherwise they stay up as long as the device is up. If you have a switch with more than one layer3 interface, and you have set up routing in a way, that the switch is still reachable for management if any of the layer3 interfaces is down but not.
But it depends on your specific topology. Dictionary Dictionary Term of the Day. Gorilla Glass. Techopedia Terms. Connect with us. Sign up. Term of the Day. Best of Techopedia weekly. News and Special Offers occasional.
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