What are the use environment and communication protocols of DNS DHCP SNMP Telnet?

DNS is a domain name resolution protocol, which can resolve domain names into ip addresses and vice versa. The port number is 53 UDP/TCP；;

DHCP is a protocol that automatically assigns ip addresses and parameters. Port numbers are 67 and 68UDP；;

SNMP is a simple network management protocol, which is used for network management. The port numbers are 160 and161UDP;

Telnet is a remote login protocol used to log in to a remote host. The port number is 23.

All are application layer protocols, I hope it will help you.