We had this question many times before. It is also worth using the search facility of CLN.
in short:loopback int - this is virtual (not phusical (programm interface))
it siting in SDRAM router and always UP and UP . his use for diffrent goals in routing ...
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 192.168.0.1/32, router 2 has the loopback 192.168.0.2/32 and so on".
Hope this answer resolves your queries.