Network Ports

20

TCP

FTP (data)

Active mode data transfer

21

TCP

FTP (control)

File transfer commands

22

TCP

SSH

Secure shell, SCP, SFTP

23

TCP

Telnet

Unencrypted — never use in production

25

TCP

SMTP

Email sending (outbound)

53

TCP/UDP

DNS

Queries (UDP), zone transfers (TCP)

67

UDP

DHCP (server)

IP address assignment

68

UDP

DHCP (client)

Client requests

69

UDP

TFTP

Trivial FTP — switch configs, PXE boot

80

TCP

HTTP

Unencrypted web traffic

88

TCP/UDP

Kerberos

Authentication protocol (AD)

110

TCP

POP3

Email retrieval

123

UDP

NTP

Time synchronization

143

TCP

IMAP

Email retrieval (server-side folders)

161

UDP

SNMP

Network monitoring (queries)

162

UDP

SNMP Trap

Network monitoring (alerts)

389

TCP/UDP

LDAP

Directory services

443

TCP

HTTPS

Encrypted web traffic

465

TCP

SMTPS

SMTP over TLS (implicit)

514

UDP

Syslog

System logging

587

TCP

SMTP (submission)

Email submission (STARTTLS)

636

TCP

LDAPS

LDAP over TLS

993

TCP

IMAPS

IMAP over TLS

995

TCP

POP3S

POP3 over TLS

1812

UDP

RADIUS (auth)

Authentication (802.1X, VPN)

1813

UDP

RADIUS (acct)

Accounting

1645

UDP

RADIUS (legacy auth)

Old RADIUS — still seen in some configs

1646

UDP

RADIUS (legacy acct)

Old RADIUS accounting

49

TCP

TACACS+

Device administration AAA