Application layer protocols based on UDP: DNS, TFTP (Simple File Transfer Protocol) and SNMP (Simple Network Management Protocol).

1, DNS: default port of domain name service: 53.

2.TFTP: Common file transfer protocol, with the default port of 69.

3.SNMP (Simple Network Management Protocol) is received through UDP port 16 1, and only trap information uses UDP port 162.

4.NTP: network time protocol, and the default port is 123.