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lwIP - lightweight TCP/IP

lwIP is a light-weight implementation of the TCP/IP protocol suite that was originally written by Adam Dunkels at the Computer and Networks Architectures (CNA) lab of the Swedish Institute of Computer Science but now is being actively developed by a team of developers distributed world-wide currently administered by Simon Goldschmidt and Dirk Ziegelmeier. The development homepage has the latest news and releases:

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

lwIP is freely available (under a BSD-style license) in C source code format and can be downloaded from the development homepage.

The focus of the lwIP TCP/IP implementation is to reduce the RAM usage while still having a full scale TCP. 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.

Since its release, lwIP has spurred a lot of interest and is today being used in many commercial products. lwIP has been ported to multiple platforms and operating systems and can be run either with or without an underlying OS.

lwIP includes the following protocols and features:

• 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
• UDP (User Datagram Protocol) including experimental UDP-lite extensions
• TCP (Transmission Control Protocol) with congestion control, RTT estimation and fast recovery/fast retransmit
• Raw/native API for enhanced performance
• Optional Berkeley-like socket API
• DNS (Domain names resolver)
• SNMP (Simple Network Management Protocol)
• DHCP (Dynamic Host Configuration Protocol)
• AUTOIP (for IPv4, conform with RFC 3927)
• PPP (Point-to-Point Protocol)
• ARP (Address Resolution Protocol) for Ethernet

Getting started

If you are new to lwIP, we recommend that you read one of the following manuals:

• lwIP Application Developers Manual, if you are new to lwIP or are trying to build an application on top of an already installed lwIP installation
• lwIP Platform Developers Manual, if you are trying to make lwIP work on your platform, with your OS, and your device driver
• lwIP Developers Manual, if you would like to delve into the innards of lwIP
• Available device drivers, to see if there is a prewritten driver available for your hardware

The following links may also be useful:

• The lwIP Savannah site, and the following subpages:
  • git source via web
  • contrib git source via web
  • the bug tracker
  • the mailing lists (be sure to join before writing to the lists)
• "Design and Implementation of the lwIP TCP/IP Stack" (obsolete, but good starting point)

Further reading

• Frequently Asked Questions
• Application notes - a miscellaneous collection of notes, thoughts, and questions deemed valuable
• Release notes - upgrade notes, feature changes or removals, etc.
  • lwIP version 1.3.0 release notes
  • lwIP version 1.3.1 release notes
  • lwIP version 1.3.2 release notes
  • lwIP version 1.4.0 release notes
• Project roadmap - ideas for the future of lwIP
• Projects that use lwIP - applications and projects that use lwIP

lwIP Application Developers Manual

1. Audience
2. Introduction to lwIP
3. Protocols
   • Link and network protocols
   • Transport protocols
   • High level protocols
     • DHCP
     • DNS
4. Application API layers
   • Raw/native API
   • Netconn API
   • Socket API
5. lwIP with or without an operating system
6. Sample lwIP applications
   • Sample Web Server
7. lwIP and multithreading
8. lwIP IPv4/IPv6 stacks
9. Initializing lwIP
   • Initialization for simple lwIP
   • Initialization using tcpip.c
   • Network interfaces management
10. Configuring lwIP
    • lwIP makefiles
    • lwipopts.h
    • lwIP code size
    • Maximizing throughput
    • Tuning TCP
    • Custom memory pools
11. Reporting bugs
12. Further lwIP support

lwIP Platform Developers Manual

1. Audience
2. Getting the code
3. Creating a platform
   • Porting for an OS (sys_arch.c/h, cc.h)
   • Writing a device driver (netif,ethernetif...)
4. Debugging lwIP

lwIP Developers Manual

1. Audience
2. Contributing to lwIP
3. lwIP modules (files, directories...)
   • lwIP functions documentation (PDF file)
   • lwIP functions documentation (HTML)
4. Architectural flow charts
   • Architectural Rx flow (PDF file)
5. Debugging lwIP