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As laid out in RFC 5942, the assumption that a dynamically assigned (SLAAC/DHCPv6) address implies an on-link subnet, is wrong. lwIP does currently make that assumption, routing packets according to local address subnets rather than the on-link prefix list. The result is that packets may not make it to their destination due to incorrect routing decisions. This patch changes the routing algorithms to be (more) compliant with RFC 5942, by implementing the following new routing policies: - all routing decisions check the on-link prefix list first, and select a default router for off-link routing only if there is no matching entry in the on-link prefix list; - dynamically assigned addresses (from address autoconfiguration) are considered /128 assignments, and thus, no routing decisions are taken based on matches against their (/64) subnet anymore; - more generally, all addresses that have a lifetime are considered dynamically assigned and thus of size /128, which is the required behavior for externally implemented SLAAC clients and DHCPv6; - statically assigned (i.e., manually configured) addresses are still considered /64 assignments, and thus, their associated subnet is considered for routing decisions, in order to behave as generally expected by end users and to retain backward compatibility; - the link-local address in IPv6 address slot #0 is considered static and thus has no lifetime and an implied /64 subnet, although link- local routing is currently always handled separately anyway. IPv6 source address selection is kept as is, as the subnet tests in the algorithm serve as poor man's longest-common-prefix equivalent there (RFC 6724 Sec. 5, Rule 8).
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>