Copy to TFTP

[hs08]

Hello,

When i try to backup the startup config to the TFTP server the result always timeout. TFTP server is reachable and the ping showing no any problem. 

Then it try issue command ip tftp source-interface loopback0 for example and the backup to the TFTP is working.

What the logic that we should issue ip tftp source-interface? I believe all my interfaces is able to reach the TFTP server.

[Flavio Miranda]

@hs08 

 Is there any firewall in between the device and the tftp server or access list on the device.

.

Keep in mind that ping and TCP communication may be treated differently on the network. 

[hs08]

hi @Flavio Miranda 

No firewall, just add ip tftp source-interface and it's worked. Seem strange for me..

[Flavio Miranda]

@hs08 which device is It?

[hs08]

Many devices, ISR4321, ISR4431, C3750.

[Flavio Miranda]

It does not make much Sense, as you realized yourself. Reasons to explain this behavior, in my opinion, relies on firewall, which you already told is not the case, or some config on the device or on the server side. 

 Basically you are right to suppose this is weird as you have connectivity to tftp server from other interface 

 Is It possible to shared the show running of one device to double check?

[hs08]

Here the config but i remove some of sensitive data such as user, password and ip address

[Flavio Miranda]

The config does not give any hint. 

One way to try to figure this out would be using wireshark capturing on loop back and do the same in a different interface to compare. 

[Leo Laohoo]

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@hs08 wrote:
Then it try issue command ip tftp source-interface loopback0 for example and the backup to the TFTP is working.

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Because there are many interfaces to choose from.  

This command is mandatory in IOS-XE even if the switch has only one interface with an IP address.

[hs08]

But what i feel strange is all interface is can reach to the TFTP server, so even we don't have ip tftp source-interface and the devices pick any random interface, this should will be fine.

[Leo Laohoo]

Classic IOS is fine without the command.  IOS-XE is different.  

Never make the mistake that classic IOS and IOS-XE are the same.  Always treat IOS-XE as a completely different OS because it is.  

Cisco is re-inventing the wheel with IOS-XE.  

[Joseph W. Doherty]

I don't recall whether the later IOS versions place TFTP into a management VRF.  If they do, using the TFTP source interface would likely get that interface into the global VRF.

[Aref Alsouqi]

What do you see if you try to tracerotue the TFTP server from one of these routers? does it take the expected path?

[hs08]

since ping is okay with or without ip tftp source-interface so all used same path.

[Aref Alsouqi]

Not necessarily. Ping requests could go one way and their replies could come another way.