TFTP or Trivial File Transfer Protocol is a simple file transfer protocol. TFTP uses UDP port 69, no authentication or encryption are supported, and directory navigation is not possible. Three file transfer methods are available: netascii (or ASCII for text files), octet (or image for binary files) and mail (not used anymore).
A TFTP client sends to the server a read request (RRW or Read ReQuest) or a write request (WRQ or Write ReQuest) using UDP protocol; destination port is 69 and source port is random (X). The TFTP server answers to the client with an ACK using a random source port (Y). Next data transfer will use only UDP ports X and Y (port 69 is not used anymore); each sent data packet (DAT) will be acknowledge (ACK).
From an IOS device, TFTP can be used as “redirection” destination:
Router#show tech-support | redirect tftp://192.168.10.1/Router_tech-support-20120819
TFTP can be used also to transfer files from and to the server:
Router#copy tftp://192.168.10.1/ios/c180x-advipservicesk9-mz.124-9.T7.bin flash:
A Cisco router can act as a TFTP server, allowing remote clients to get local stored files:
Each local file must be declared as a TFTP file.