lwIP

"lwIP (lightweight IP) is a widely used open source TCP/IP stack designed for embedded systems. lwIP was originally developed by Adam Dunkels at the Swedish Institute of Computer Science and is now developed and maintained by a worldwide network of developers.

The focus of the lwIP TCP/IP implementation is to reduce resource usage while still having a full-scale TCP.^[3] This makes lwIP suitable for use in embedded systems with tens of kilobytes of free RAM and room for around 40 kilobytes of code ROM.

The features:

Internet layer

• IP (Internet Protocol) including packet forwarding over multiple network interfaces
• ICMP (Internet Control Message Protocol) for network maintenance and debugging
• IGMP (Internet Group Management Protocol) for multicast traffic management

Transport layer

• UDP (User Datagram Protocol) including experimental UDP-Lite extensions
• TCP (Transmission Control Protocol) with congestion control, RTT estimation and fast recovery/fast retransmit

Application layer

• DNS (Domain Name System)
• SNMP (Simple Network Management Protocol)
• DHCP (Dynamic Host Configuration Protocol)

Link layer

• PPP (Point-to-Point Protocol)
• ARP (Address Resolution Protocol) for Ethernet

Other

• Specialized raw/native API for enhanced performance
• Optional Berkeley-like socket API
• AUTOIP / Link-local address (for IPv4, conforms with RFC 3927)

https://en.wikipedia.org/wiki/LwIP

https://savannah.nongnu.org/projects/lwip/

https://en.wikipedia.org/wiki/UIP_%28micro_IP%29