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Networking

The Internet is an interconnected collection of separate IPv4 and IPv6 networks, all communicating over a series of standardised protocols conceptualised in the OSI model. Traffic is routable between these separate networks.

Types of network

  • A LAN, or Local Area Network, refers to a single site.
  • WLAN refers to a Wireless LAN.
  • WAN, or Wide Area Network, typically refers to a network of LANs connected across the Internet via a VPN or via a private backbone.
  • PAN refers to a Personal Area Network, e.g. a mobile hotspot.

Transports

There are two commonly used transports on the Internet today:

  • TCP/IP provides reliable, ordered transmission of segments over sessions.
  • UDP offers lighter weight communication with lesser delivery guarantees.

Ports

Ports are used to expose multiple services from the same host address. They're grouped into defined ranges:

  • Source ports assigned to clients for sessions are in the ephemeral range (49,152–65,535)
  • Well-known ports between 0–1,023
  • Registered port numbers between 1,024–49,151

Common port numbers

More common services can be located in /etc/services on most BSD, Linux and Unix systems.

Port numberServiceDependencies
20FTP (data)TCP
21FTP (command)TCP
22SFTPTCP
22SSHTCP
23TelnetTCP
25SMTP (insecure)TCP
67DHCP (server)UDP
68DHCP (client)UDP
69TFTPUDP
80[[HTTPnet.http]]TCP
110POP3 (insecure)TCP
135Windows RPCTCP/UDP
143IMAPTCP
389LDAPTCP/UDP
443HTTPSTCP
445SMBTCP
587SMTP (secure)TCP
636LDAPsTCP
993IMAP (secure)TCP
995POP3 (secure)TCP
1433SQL Server (default instance)TCP
1434SQL Server (dedicated admin connection)TCP
1434SQL Server (browser service)UDP
2376Docker engineTCP
3306MySQLTCP
5432PostgreSQLTCP/UDP

Children

  1. 5-tuple
  2. DNS
  3. Ethernet
  4. HTTP
  5. IPv4
  6. IPv6
  7. OSI model
  8. Protocol Buffers
  9. TCP
  10. Topologies
  11. UDP
  12. gRPC