Port Number

Each single network node can run multiple applications that use the same network interface, and therefore use the same IP address. For example, an RTOS application can run a TFTP server, an echo server and a Nabto client at the same time - all of which make use of the TCP/IP stack. Different applications running on the same network node, and therefore at the same IP address, are identified by their port number.

The source and destination address of each TCP or UDP packet is therefore a combination of an IP address and a port number. The IP address identifies the node on the network and the port number identifies the application within the node (see sockets).

Useful links:

• TCP/IP Networking Basics
• FreeRTOS+TCP networking tutorial

Other networking basics pages:

• Ethernet Networking and Addressing
• MTU - Maximum Transmission Unit
• IP Networking
• IP Network Addressing
• ARP - Address Resolution Protocol
• Subnets / Netmasks
• Gateways and Routers
• UDP Networking
• TCP Networking
• MSS - Maximum Segment Size
• Port Numbers
• Sockets
• Binding
• Clients and Servers
• Static IP Addresses
• DHCP - Dynamic Host Control Protocol
• Name Resolution
• DNS - Domain Name Service
• LLMNR - Link-local Multicast Name Resolution
• NBNS - NetBIOS Name Service
• Bytes Order and Endian