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This patch adds full support for IPv6 address scopes, thereby aiming to be compliant with IPv6 standards in general and RFC 4007 in particular. The high-level summary is that link-local addresses are now meaningful only in the context of their own link, guaranteeing full isolation between links (and their addresses) in this respect. This isolation even allows multiple interfaces to have the same link-local addresses locally assigned. The implementation achieves this by extending the lwIP IPv6 address structure with a zone field that, for addresses that have a scope, carries the scope's zone in which that address has meaning. The zone maps to one or more interfaces. By default, lwIP uses a policy that provides a 1:1 mapping between links and interfaces, and considers all other addresses unscoped, corresponding to the default policy sketched in RFC 4007 Sec. 6. The implementation allows for replacing the default policy with a custom policy if desired, though. The lwIP core implementation has been changed to provide somewhat of a balance between correctness and efficiency on on side, and backward compatibility on the other. In particular, while the application would ideally always provide a zone for a scoped address, putting this in as a requirement would likely break many applications. Instead, the API accepts both "properly zoned" IPv6 addresses and addresses that, while scoped, "lack" a zone. lwIP will try to add a zone as soon as possible for efficiency reasons, in particular from TCP/UDP/RAW PCB bind and connect calls, but this may fail, and sendto calls may bypass that anyway. Ultimately, a zone is always added when an IP packet is sent when needed, because the link-layer lwIP code (and ND6 in particualar) requires that all addresses be properly zoned for correctness: for example, to provide isolation between links in the ND6 destination cache. All this applies to packet output only, because on packet input, all scoped addresses will be given a zone automatically. It is also worth remarking that on output, no attempt is made to stop outgoing packets with addresses for a zone not matching the outgoing interface. However, unless the application explicitly provides addresses that will result in such zone violations, the core API implementation (and the IPv6 routing algorithm in particular) itself will never take decisions that result in zone violations itself. This patch adds a new header file, ip6_zone.h, which contains comments that explain several implementation aspects in a bit more detail. For now, it is possible to disable scope support by changing the new LWIP_IPV6_SCOPES configuration option. For users of the core API, it is important to note that scoped addresses that are locally assigned to a netif must always have a zone set; the standard netif address assignment functions always do this on behalf of the caller, though. Also, core API users will want to enable LWIP_IPV6_SCOPES_DEBUG at least initially when upgrading, to ensure that all addresses are properly initialized. |
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INTRODUCTION
lwIP is a small independent implementation of the TCP/IP protocol
suite that has been developed by Adam Dunkels at the Computer and
Networks Architectures (CNA) lab at the Swedish Institute of Computer
Science (SICS).
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.
FEATURES
* 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)
* 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)
APPLICATIONS
* HTTP server with SSI and CGI
* SNMPv2c agent with MIB compiler (Simple Network Management Protocol)
* SNTP (Simple network time protocol)
* NetBIOS name service responder
* MDNS (Multicast DNS) responder
* iPerf server implementation
LICENSE
lwIP is freely available under a BSD license.
DEVELOPMENT
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/yarrick/lwip-merged
DOCUMENTATION
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/
There is now a constantly growing wiki about lwIP at
http://lwip.wikia.com/wiki/LwIP_Wiki
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/
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.
Adam Dunkels <adam@sics.se>
Leon Woestenberg <leon.woestenberg@gmx.net>