I have written a script in python, always with scapy, that captures in real time all the Telnet traffic accross the network.
The script, when reduced to its minimal needs, has 18 lines …
Here is the video.
All the datas captured are stored in a file: Client-Source IP – Server-Destination IP
The script does not manage very well when several telnet connections are launched to the same Telnet server by a unique host.