Assuming you're wanting to know the flow when you request the configuration to be TFTP'd to a server using SNMP, then this is how it works.
1. The SNMP manager does an SNMP SET request (or multiple SET requests) of objects in the CISCO-CONFIG-COPY-MIB (thus SNMP read-write is required).
2. The agent (device) initiates a TFTP write-request to the specified TFTP server using the specified filename.
3. The write-request is processed by the TFTP server on udp/69. The TFTP server then responds to the agent's source UDP port with a new ephemeral UDP port on the server.
4. The agent begins to send data using its original UDP source port, and the new UDP destination port on the server.
