FTP traffic configured to use Interface Loopback

[Sparkeyluv_357]

Why would someone configure FTP to  use interface Loop back within a routers configuration?

Example:

Why would someone configure a routers FTP to use a loop back address?

interface Loopback0

description Loopback interface

ip address x.x.x.x x.x.x.x

no ip directed-broadcast

!

...

ip telnet source-interface Loopback0

ip tftp source-interface Loopback0

ip ftp source-interface Loopback0

[Giuseppe Larosa]

Hello,

the loopback interface is a logical interface that is always up/up if the device is alive.

The loopback interface has to be advsertised and this is the only drawback.

Using a loopback interface is so the better way to make the device to use the same Source IP address in accessing services like an FTP server and so on like for example a Radius or Tacacs+ server.

So when reviewing activity logs you can always be sure that IP 10.1.1.1 means that specific router and not another one.

Loopback interfaces are also very important in networking for example for internal BGP and MPLS and all MPLS based services.

Without setting those  source commands the router would use the interface in the path to the destination, that can change for different destinations and can change over time if the primary interface goes down.

Hope to help

Giuseppe

[Sparkeyluv_357]

So from what i'm gathering in your post, Loopback interfaces are used

As they are always active (up/up)

It can use its self as the source for FTP/Tacacs+ and other services

Ease of verifying its self as the source within logs

Am I correct?

[Giuseppe Larosa]

Hello,

yes your understanding is correct

Hope to help

Giuseppe

[Joseph W. Doherty]

"It can use its self as the source for FTP/Tacacs+ and other services"

Hopefully you understand the "other services", but for example other devices can use an ACL (or FW rules) to block, or not, traffic using the loopback IP. Also, loopbacks aren't just for traffic sourced from the device they are often used as a management IP for the device too.