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So far, the UDP core module implemented only IPv4 multicast support. This patch extends the module with the features necessary for socket layers on top to implement IPv6 multicast support as well: o If a UDP PCB is bound to an IPv6 multicast address, a unicast source address is selected and used to send the packet instead, as is required (and was the case for IPv4 multicast already). o Unlike IPv4's IP_MULTICAST_IF socket option, which takes a source IPv4 address, the IPV6_MULTICAST_IF socket option (from RFC 3493) takes an interface identifier to denote the interface to use for outgoing multicast-destined packets. A new pair of UDP PCB API calls, udp_[gs]et_multicast_netif_index(), are added to support this. The new definition "NETIF_NO_INDEX" may be used to indicate that lwIP should pick an interface instead. IPv4 socket implementations may now also choose to map the given source address to an interface index immediately and use the new facility instead of the old udp_[gs]et_multicast_netif_addr() one. A side effect of limiting the old facility to IPv4 is that for dual- stack configurations with multicast support, the UDP PCB size is reduced by (up to) 16 bytes. o For configurations that enable loopback interface support, the IPv6 code now also supports multicast loopback (IPV6_MULTICAST_LOOP). o The LWIP_MULTICAST_TX_OPTIONS opt.h setting now covers both IPv4 and IPv6, and as such is no longer strictly linked to IGMP. It is therefore placed in its own lwIP options subgroup in opt.h. The IPV6_MULTICAST_HOPS socket option can already be implemented using the existing IP_MULTICAST_TTL support, and thus requires no additional changes. Overall, this patch should not break any existing code.
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>