Loopback interface

Nawakette

Hi !

Could you please tell me what is the main reasons for using loopback interfaces (except to "ping yourself") ?

Thanks...

jescab

I use it for the first step in diagnostics.

BubbaJ

A loopback interface never goes down (unless you shut it down). You can reference it from other devices if you include it in your routing protocol. This may allow you to still get to the router if the directly connected interface goes down. Certain protocols like OSPF will use the highest loopback as the router ID since a loopback is the most stable type of interface.

It is also useful to create different networks for practice.

marlon23

when you have half-duplex mode on ethernet and sending data, internal loopback is used for detecting collissions (when there is something else on loopback interface than you are transmitting - there is a collision)
if you are using full-duplex feature, you have to disable internal loopback becouse there can be simultaneous data transfer and btw. there are no such thing as collisions in full-duplex.

routing protocols contra loopback was mentioned before

EdTheLad

Hi Marlon, he was asking about the virtual loopback interfaces configurable via cli.The loopback regarding eth ports that you have mentioned is fictional.You must have read this in an old rfc,the author of the rfc states
that he is giving a general description not fact.The sending device monitors the voltage levels of the line and when the voltage level increases above a threshold due to the extra signal a collision is flaged.Nothing to do with loopbacks.

marlon23

my mistake, sorry

unwritt3n

We've also used Loopbacks with configuring NAT in out Networking Academy lab.