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New Member

TFTP between subnets

A group of clients on our network are configured to PXE boot off the network to obtain their desktop images. During boot, the clients obtain the following information from a DHCP Server:

Client IP address

Gateway IP address

TFTP server IP address

Bootstrap file name


If the clients are located on the same subnet as the TFTP server, they are able to download the bootstrap file via TFTP and connect to the boot server to boot their desktop image.

If the clients are located on a different subnet than the TFTP server, the clients are not able to download the bootstrap file via TFTP.

Packet traces taken from both the client and server subnets show the TFTP requests sent from the clients to the TFTP server, but the requests do not reach the TFTP server.

Is there a particular command(s) that needs to be entered on a Cisco router to allow TFTP unicast packets to traverse the router?


Ardence Support

New Member

Re: TFTP between subnets

You could try adding an IP helper address that points to your tftp server....

in my network the TFTP is also the DHCP.. so my helper allows both

New Member

Re: TFTP between subnets

Thanks, we use the IP helper for the DHCP server on a different subnet and that works, but we were not sure since the TFTP request is a unicast packet, not a broadcast packet like the one sent initially to the DHCP server.

We'll add the IP helper command and test.

Thanks again.

Re: TFTP between subnets


As long as the TFTP Server also incorporates the DHCP and / or BOOTP servers it would work, because the IP Helper is nothing but a DHCP Relay Agent.

All the best and please share your results too.


Wilson Samuel

Hall of Fame Super Silver

Re: TFTP between subnets

If the TFTP packets are unicast, as the original poster says they are, then ip helper-address will not solve this because helper-address only helps with broadcast.

There are a couple of things that I would suggest to check:

- is the client getting the correct default gateway address from the DHCP server?

- is the client getting the correct subnet mask from the DHCP server?

- does the default gateway have a correct route to the TFTP server?

- does the TFTP server have a correct route back to the subnet where the clients are?