Can't TFTP 2900 router configuration

[mahmoud youssef]

I have cisco 2900 routet. loopback0  interface is configured as the source interface of tftp. when I try to tftp the router configuration to my labtop and error message appears "/error opening tftp:"

But when i configured interface g0/0 which is connected to my labtop as the source tftp it does work. my quetion is why do we configure loopback interface as source tftp?!. and what will be my labtop ip address then?!

[Reza Sharifi]

You don't have to configure the source interface. The source interface (lo0) in this case is used because lo0 is a logical interface and never goes down vs a physical interface can go down and disconnect the tftp session. This is just an optional command.

what will be my labtop ip address then?!

The laptop IP address should be in the same segment as interface g0/0.

HTH

[mahmoud youssef]

First, Thanks for your reply. But my understanding regarding this regard is not much more than knowing some little configuration commands. My request from you is to:

1) describe why I need the source IP interface for tftp?!. appreciate if you could attache a picture for packet, frame...etc

2) When I connected my laptop to g0/0 I get this error message "%error opening tftp...etc". Although I disabled my firewall.

3) What do you mean by optional command. Is this mean that if I don't add this command to the configuration the copying does work?!

N.B: I have attached the router configuration.

[Reza Sharifi]

Hi,

3) What do you mean by optional command. Is this mean that if I don't add this command to the configuration the copying does work?!

Yes, that command is optional meaning you don't need in order for tftp to work with your router.

Looking at your config, interface g0/0 seems to be connected to something and interface g0/1 is unused.

interface GigabitEthernet0/1
  description UNUSED
  no ip address
  shutdown
  duplex auto
  speed auto

So, connect the tftp server to interface g0/1 and give one IP to your tftp server and one to the interface and try again.

HTH

[mahmoud youssef]

I did configured g0/1 and connected my laptop to it but when I'm trying to copy to the tftp server in my laptop it doesn't work and gave me the error message "%error opening tftp...etc" . However, I did issued the command "ip tftp source-interface g0/1" and then the copying successfully executed. and the uploaded file is the result. :)

This action made me confused and wanted to understand What is this command? and the biggest confusion came when I saw the "loopback 0" configured as tftp source address. what is the effect will happen when I configure the loopback as the source IP. why it didn't work untill I made the g0/1 the source tftp interface?. and al lot of questions?. The aim of this post is to understand the mechanism and to understand the WHY?. I would appreciate your support concerning this matter if you can provide detailed description.

Thanks 

[Reza Sharifi]

Excellent, so you got it working. As for lo0 as tftp source, it is used because interface lo0 is a logical interface. Right now the source interface is g0/1. So, for some reason if you change the interface and connect the tftp server to g0/0 or 0/2, etc.. the tftp will not work and so you have to change the tftp source interface to match g0/0 or 0/2, etc..

So, when you use lo0, as the source, you never have to worry about changing the source any more because lo0 will always be present in your router. Also, here is a link for more info:

http://www.firewall.cx/cisco-technical-knowledgebase/cisco-routers/882-cisco-ip-tftp-source-interface.html

HTH 

[mahmoud youssef]

First, you told me a previous reply that this command is optional. So this means that if issue the command "no ip tftp source-interface xxx" the tftp works normally.!

Second, In your opinion why didn't tftp worked successfully when the source was the loopback0?!

Thanks