lwIP is a small independent implementation of the TCP/IP protocol suite.
The focus of the lwIP TCP/IP implementation is to reduce the RAM usage while still having a full scale TCP. This making lwIP suitable for use in embedded systems with tens of kilobytes of free RAM and room for around 40 kilobytes of code ROM.
lwIP was originally developed by Adam Dunkels at the Computer and Networks Architectures (CNA) lab at the Swedish Institute of Computer Science (SICS) and is now developed and maintained by a worldwide network of developers.
IP (Internet Protocol, IPv4 and IPv6) 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
MLD (Multicast listener discovery for IPv6). Aims to be compliant with RFC 2710. No support for MLDv2
ND (Neighbor discovery and stateless address autoconfiguration for IPv6). Aims to be compliant with RFC 4861 (Neighbor discovery) and RFC 4862 (Address autoconfiguration)
DHCP, AutoIP/APIPA (Zeroconf), ACD (Address Conflict Detection) and (stateless) DHCPv6
UDP (User Datagram Protocol) including experimental UDP-lite extensions
TCP (Transmission Control Protocol) with congestion control, RTT estimation fast recovery/fast retransmit and sending SACKs
raw/native API for enhanced performance
Optional Berkeley-like socket API
TLS: optional layered TCP (“altcp”) for nearly transparent TLS for any TCP-based protocol (ported to mbedTLS) (see changelog for more info)
PPPoS and PPPoE (Point-to-point protocol over Serial/Ethernet)
DNS (Domain name resolver incl. mDNS)
6LoWPAN (via IEEE 802.15.4, BLE or ZEP)
HTTP server with SSI and CGI (HTTPS via altcp)
SNMPv2c agent with MIB compiler (Simple Network Management Protocol), v3 via altcp
SNTP (Simple network time protocol)
NetBIOS name service responder
MDNS (Multicast DNS) responder
iPerf server implementation
MQTT client (TLS support via altcp)
lwIP is freely available under a BSD license.
lwIP has grown into an excellent TCP/IP stack for embedded devices, and developers using the stack often submit bug fixes, improvements, and additions to the stack to further increase its usefulness.
Development of lwIP is hosted on Savannah, a central point for software development, maintenance and distribution. Everyone can help improve lwIP by use of Savannah’s interface, Git and the mailing list. A core team of developers will commit changes to the Git source tree.
The lwIP TCP/IP stack is maintained in the ‘lwip’ Git module and contributions (such as platform ports) are in the ‘contrib’ Git module.
See doc/savannah.txt for details on Git server access for users and developers.
The current Git trees are web-browsable: http://git.savannah.gnu.org/cgit/lwip.git http://git.savannah.gnu.org/cgit/lwip/lwip-contrib.git
Submit patches and bugs via the lwIP project page: http://savannah.nongnu.org/projects/lwip/
Continuous integration builds (GCC, clang): https://travis-ci.org/lwip-tcpip/lwip
Self documentation of the source code is regularly extracted from the current Git sources and is available from this web page: http://www.nongnu.org/lwip/
Also, there are mailing lists you can subscribe at http://savannah.nongnu.org/mail/?group=lwip plus searchable archives: http://lists.nongnu.org/archive/html/lwip-users/ http://lists.nongnu.org/archive/html/lwip-devel/
There is a wiki about lwIP at http://lwip.wikia.com/wiki/LwIP_Wiki You might get questions answered there, but unfortunately, it is not as well maintained as it should be.
lwIP was originally written by Adam Dunkels: http://dunkels.com/adam/
Reading Adam’s papers, the files in docs/, browsing the source code documentation and browsing the mailing list archives is a good way to become familiar with the design of lwIP.