Hi I have some weard port utilization. My CCM (tftp service is active) is trying to communicate with an IPPhone 7912 on UDP\15448,UDP\11787, UDP\6633 or UDP\2201. Do ou know why ? That's append when the end user try to change the ringtone of his 7912.
TFTP uses arbitrary negotiated port numbers for file transfers. The first request will go from an arbitrary assigned UDP port on the client to UDP port 69 on the server. The actual file transfer will use a different arbitrary choosen port on the TFTP server to the client port.
This could explain the observed behavior.
Hope this helps! Please rate all posts.
P.S.: details are found in RFC 1350, which states about the UDP ports used (they talk about TID, but this is in effect the same):
"A requesting host chooses its source TID as described above, and sends its initial request to the known TID 69 decimal (105 octal) on the serving host. The response to the request, under normal operation, uses a TID chosen by the server as its source TID and the TID chosen for the previous message by the requestor as its destination TID.
The two chosen TID's are then used for the remainder of the transfer."
you should have mentioned PIX in the original post. The PIX can use stateful inspection of TFTP by monitoring the port negotiation and will open the proper port for the file transfer. The command you found "inspect tftp" enables this behaviour (like for other protocolls as well, f.e. SIP, FTP and so on).
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