Blocking TCP port 69 also blocks TFTP

Hello guys,

I have a basic question, although a little tricky for me to understand. I was configuring some ACLs on a router, here is the thing I was trying to block TFTP traffic but by mistake I block TCP 69 port instead of UDP 69, both configuration successfully blocks TFTP. But here is the question, how come that blocking TCP:69 also blocks TFTP as TFTP works on UDP:69?

Thanks in advance. : ).

TFTP Uses Some features of the TCP Stack such as acknowledgments, so by blocking tcp on port 69 you are effectivly stopping tftp from be able to establish a proper session with the host.


There are a few applications that use both TCP and UDP like BOOTP, DNS, NFS, SNMP.

Although it is not specifically stated in the RFC for TFTP is is however the case.

Thanks