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Resolving Cisco Router/Switch Tftp Problems: Source IP Address - The 'IP TFTP Source-Interface' Command

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When working with Cisco equipment that has multiple ip interfaces, a common problem engineers are faced with is trying to successfully tftp to or from the Cisco device. This issue is usually encountered when the Cisco device (router or multi-layer switch) uses a different source IP address which cannot reach our TFTP Server's IP address or is blocked due to access lists.

cisco-ip-tftp-source-interface-1Figure 1. The tftp source IP problem with tftp and other services on a Cisco Router

Luckily, there is a way around this problem, and it’s a simple one.

Note: The commands used are identical for all Cisco routers and Catalyst switches.

To ensure your Cisco router or multi-layer switch uses the correct interface during any tftp session, use the ip tftp source-interface command to specify the source-interface that will be used by the device.

The following example instructs our Cisco 3750 Layer 3 switch to use VLAN 5 interface as the source ip interface for all tftp sessions:

3750G-Stack(config)# ip tftp source-interface vlan 5

As shown below, VLAN 5 has IP address assigned to it, therefore this IP address will be the source interface from now on:

3750G-Stack# show ip interface brief
Interface  IP-Address      OK? Method Status    Protocol
Vlan1    YES NVRAM  up           up     
Vlan2   YES NVRAM  up           up     
Vlan3   YES NVRAM  up           up     
Vlan4    YES NVRAM  up           up     
Vlan5   YES NVRAM  up           up     
Vlan6   YES NVRAM  up           up     
Vlan7   YES NVRAM  up           up     
Vlan8   YES NVRAM  up           up

Your IP address:

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