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kamal el assaad
Beginner

loopback

what is loopback? what is the purpose of a loopback? and it use the highest ip interface or also any available loopguared in the network?

1 ACCEPTED SOLUTION

Accepted Solutions
parents95
Beginner

Hi,

 

A loopback interface is a logical interface.

This means that is not related to any hardware "feature" (cable connections, speed, duplex,...).

 

It can be configured with an IP address like a normal physical interface.


It is always up/up.

 

Purpose: as I've said, it is not related to any hardware feature/problem so it is always reachable since there is at least one physical interface up/up on the device (and obviously a route to it).


It can be used in different topics: router-id, ip helper to loopback address insted of physical address of DHCP server, ... and others.

 

"and it use the highest ip interface or also any available loopguared in the network?": I think you have written the general rule used to elect RID in routing protocols, such as in OSPF.

RID is selected as the highest loopback interfaces' ip address, if no loopback exists it is used the highest ip address of physical interfaces.

 

Luca

View solution in original post

3 REPLIES 3
parents95
Beginner

Hi,

 

A loopback interface is a logical interface.

This means that is not related to any hardware "feature" (cable connections, speed, duplex,...).

 

It can be configured with an IP address like a normal physical interface.


It is always up/up.

 

Purpose: as I've said, it is not related to any hardware feature/problem so it is always reachable since there is at least one physical interface up/up on the device (and obviously a route to it).


It can be used in different topics: router-id, ip helper to loopback address insted of physical address of DHCP server, ... and others.

 

"and it use the highest ip interface or also any available loopguared in the network?": I think you have written the general rule used to elect RID in routing protocols, such as in OSPF.

RID is selected as the highest loopback interfaces' ip address, if no loopback exists it is used the highest ip address of physical interfaces.

 

Luca

View solution in original post

Martin L
VIP Advocate


Lots of uses for loopback interface; I used to use it to mimic or represent another network on the routers in my home lab. When you have lab with real Cisco routers, adding PCs on different networks can be tricky; adding several loopbacks -each in different network/subent - could save resources and space.
In my current virtual lab, I also can add loopack with /24 network and advertise it into domain. it will save resources instead of adding a router as a host.

https://www.omnisecu.com/cisco-certified-network-associate-ccna/what-is-loopback-interface-in-a-router.php

see
https://learningnetwork.cisco.com/s/question/0D53i00000KsxaLCAR/loopback-interfaces

https://learningnetwork.cisco.com/s/question/0D53i00000Kt0y0CAB/loopback-interfaces

https://learningnetwork.cisco.com/s/question/0D53i00000Kt1ufCAB/why-we-create-loopback-interface-on-routers