Scan the server 2 - tftp and snmp

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In Scan the server 2, in Footprinting & Scanning. Why can we assume that it is a tftp server?
In the solution just say “Given that we have discovered that UDP ports 177 and 234 are running a DNS and SNMP server respectively, we can assume that port 134 is running the TFTP server.”
I looked up for a relation but i couldnt find anything.

Thank you