Documentation/networking/udplite.rst

1 .. SPDX-License-Identifier: GPL-2.0
4 The UDP-Lite protocol (RFC 3828)
8   UDP-Lite is a Standards-Track IETF transport protocol whose characteristic
9   is a variable-length checksum. This has advantages for transport of multimedia
14   For in-depth information, you can consult:
16    - The UDP-Lite Homepage:
17      http://web.archive.org/web/%2E/http://www.erg.abdn.ac.uk/users/gerrit/udp-lite/
21    - The UDP-Lite HOWTO on
22 …http://web.archive.org/web/%2E/http://www.erg.abdn.ac.uk/users/gerrit/udp-lite/files/UDP-Lite-HOWT…
24    - The Wireshark UDP-Lite WiKi (with capture files):
27    - The Protocol Spec, RFC 3828, http://www.ietf.org/rfc/rfc3828.txt
33   Several applications have been ported successfully to UDP-Lite. Ethereal
34   (now called wireshark) has UDP-Litev4/v6 support by default.
36   Porting applications to UDP-Lite is straightforward: only socket level and
43   UDP-Lite provides a connectionless, unreliable datagram service and hence
44   uses the same socket type as UDP. In fact, porting from UDP to UDP-Lite is
56   With just the above change you are able to run UDP-Lite services or connect
57   to UDP-Lite servers. The kernel will assume that you are not interested in
71       Of each packet only the first 20 bytes (plus the pseudo-header) will be
72       checksummed. This is useful for RTP applications which have a 12-byte
78       This option is the receiver-side analogue. It is truly optional, i.e. not
88   The calls to getsockopt(2) are analogous. Being an extension and not a stand-
92   A detailed discussion of UDP-Lite checksum coverage options is in section IV.
103       for UDP-Lite header fields and protocol constants
112   Ready-made header files for various distros are in the UDP-Lite tarball.
145   On both sender and receiver, checksumming will always be performed
160   of UDP-Lite packets is determined by the size of the send buffer. The
167   Given a payload size larger than the send buffer size, UDP-Lite will
171   The precise value also depends on the interface MTU. The interface MTU,
173   UDP-Lite packet is split into several IP packets, of which only the
176   The send buffer size has implications on the checksum coverage length.
182   UDP-Lite will ship the 1536 bytes in two separate packets::
187   The coverage packet covers the UDP-Lite header and 848 bytes of the
190   length. The kernel always re-adjusts the coverage length to the packet
193   As an example of what happens when one UDP-Lite packet is split into
199     +-+-----------+--------------+--------------+--------------+
201     +-+-----------+--------------+--------------+--------------+
206   The UDP-Lite module generates one 1032 byte packet (1024 + 8 byte
220     Fragment 1: 1280 bytes carrying  1232 bytes of UDP-Lite data
221     Fragment 2: 1280 bytes carrying  1232 bytes of UDP-Lite data
222     Fragment 3:  948 bytes carrying   900 bytes of UDP-Lite data
225   fragment only 598 (= 3062 - 2*1232) bytes are checksummed.
228   are (annoyingly) rare: UDP-Lite is designed for optimising multimedia
232 5. UDP-Lite Runtime Statistics and their Meaning
236   level.  Live statistics about UDP-Lite are available in /proc/net/snmp
239 			    netstat -svu
241   This displays UDP-Lite statistics variables, whose meaning is as follows.
249    InErrors         Number of erroneous UDP-Lite packets. Errors include:
268   There is packet match support for UDP-Lite as well as support for the LOG target.
271     udplite 136     UDP-Lite        # UDP-Lite [RFC 3828]
275 	      iptables -A INPUT -p udplite -j LOG
282   The UDP-Lite patch was developed at