There are many TFTP implementations available in the
web so why did I write this script?
Well. It is a very good exercise. It's a simple
protocol so it's an affordable project. You have to implement the client side
and, why not? the server side.
But there is a deeper reason for this. It's just
a first step. If you check the script's help you will notice you can change the
UDP port for the connections. Using a nonstandard port will allow you to use it
even if there is another TFTP server running in your computer. You can also
hide the server. Or even you can try to bypass a firewall using an open port
like DNS or so.
Right. I'm thinking about security.
Changing the UDP port will only work for a simple
firewall, if a simple ACL (Access Control List) can be considered as a
firewall. I do.
A more advanced firewall may do deep protocol
inspection so if you try to use port 53 it will not work. But what will happen
if there are other nonstandard ports open? Or even there are some standards
ports open as port 7 (UDP ECHO)?
Not concerned? Well, this is just a TFTP and you need
to have the script running at both sides of the firewall. On the other hand
many times the information to be transferred does not need to be long and many
servers today can run a python script which is no more than a text file.
The next step is moving to use ICMP instead UDP. I
leave this for the next release if I ever publish it.
Does your firewall allow 'ping'?
Have fun, stay legal.
