Telnet is an application layer protocol (Layer 7). Its functionality is similar to any of the layer 7 protocols, including DHCP, DNS, FTP, etc.
what osi layers use telnet connections for remote use
FTP and Telnet are considered OSI layer 7 protocols. If you are blocking the service, then layer 3 or 4 (network or transport) is responsible.
23
TELNET operates at Application Layer in TCP/IP Model. It's an Application to establish a connection to TCP Port Number 23, where a Telnet server application (telnetd) is listening.
Networking layer of the OSI model
The firewall blocks it. Almost all router have telnet port blocked because it's considered dangerous.
TCP/IP because the osi model has seven layer but in tcp/ip only four layers and most important is that the tcp/ip model is reduce the function of osi model.
TELNET
Physical Layer
that layer
OSI
physical and data link