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e0c5e1988f
In summary, this patch aims to resolve bugs #47923 and #48162, by decoupling address autoconfiguration from the on-link prefix list, since those are not related. Important necessary changes are needed to meet this goal, ultimately bringing the lwIP ND6 implementation closer to compliance with RFC 4862. The main changes are: 1. support for address lifetimes, and, 2. addition of a new DUPLICATED address state. The decoupling implies that the prefix list can no longer be used to maintain state for address autoconfiguration. Most importantly, the lifetime of each address, which was previously derived from the prefix slot's lifetime, must now be associated with the address itself. This patch implements address lifetime tracking, maintaining both a valid and a preferred lifetime for each address, along with the corresponding address state changes (e.g., between PREFERRED and DEPRECATED), all as required by RFC 4862. The support for address lifetimes can be enabled with a new LWIP_IPV6_ADDRESS_LIFETIMES setting in lwipopts.h. It is required for autoconfiguration and enabled by default if autoconfiguration is enabled as well, but it may also be enabled separately, so as to allow application-controlled lifetime management (e.g., if autoconfiguration is implemented in a separate application). A special valid-lifetime of zero is used to denote a static address--that is, an address that was configured manually, that does not have lifetimes, and that should be left alone by the autoconfiguration functionality. Addresses assigned without setting a lifetime are deemed static, thus preserving compatibility with existing lwIP-based applications in this respect. Similarly, the decoupling implies that the prefix list can no longer be used to remember cases of address duplication. Previously, the detection of a duplicated address would simply result in removal of the address altogether. Instead, this patch introduces a new state "DUPLICATED", indicating that the address, while technically still present, has been found to conflict with other node addresses, and no attempt should be made to produce an autoconfiguration address for that prefix. Manually added addresses, including the link-local address, once set to DUPLICATED, will remain in that state until manual intervention. Autoconfigured DUPLICATED addresses will expire according to their valid-lifetime, essentially preserving the current behavior but without the use of the prefix list. As a first attempt to approach compliance with RFC 4862 Sec. 5.4.5, if the link-local address is detected to be duplicated, all derived addresses are marked duplicated as well, and no new addresses will be autoconfigured. More work is to be done for full compliance with that section, however. Together, those two main changes indeed do fully decouple address autoconfiguration from the on-link prefix list. Changes to the latter thus no longer affect the former, resolving bug #47923. Moreover, as a result, autoconfiguration can, and does, now also take place on advertised prefixes that do not have the on-link flag set, resolving bug #48162. The routing changes mentioned in the discussion of that bug are left to a separate patch, though. |
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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>