weblog d’un abbe

20060207

Tricky TFTP

Filed under: Experiences — abbe @ 1212

Yesterday, I was setting up firewall for my dad’s office’s server, I came to know about TFTP details (see RFC 1350). In short TFTP (read request) works as follows:

  1. Client connects (oops. it is UDP so no connects but sends datagram) to port 69 (i.e. TFTP port) of server requesting the file.
  2. Server replies to the client from other port (randomly chosen, so that the probability that the same number is chosen twice in immediate succession is very low), let’s call it φ.
  3. After then all communications with server from that client happen over port φ.

So, it’s very hard to decide what ports should remain open in firewall. One solution to start server with a fixed port range to be used for TFTP. Anyways, if u know what I want, please post it here… ;-).

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