TFTP – not that trivial protocol

TFTP, the Trivial File Transfer Protocol isn’t as trivial as it seems. It turns out that while TFTP requests are sent to UDP port 69, the responses do not need to be sourced from UDP port 69 (proof)! Because of that, some firewalls may have problems with passing such traffic – in the case of Cisco routers, enabling TFTP inspects is necessary (reflexive ACLs won’t work):

Router(config)# ip inspect name inspect_out tftp
Router(config)# interface FastEthernet 0/0
Router(config-if)# ip inspect inspect_out out

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