.\" Copyright (c) 2008 by Gerrit Renker <gerrit@erg.abdn.ac.uk>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" $Id: udplite.7,v 1.12 2008/07/23 15:22:22 gerrit Exp gerrit $
.\"
.TH udplite 7 2023-02-10 "Linux man-pages 6.05.01"
.SH NAME
udplite \- Lightweight User Datagram Protocol
.SH SYNOPSIS
.nf
.B #include <sys/socket.h>
.\" FIXME . see #defines under `BUGS',
.\"        when glibc supports this, add
.\"        #include <netinet/udplite.h>
.PP
.B sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDPLITE);
.fi
.SH DESCRIPTION
This is an implementation of the Lightweight User Datagram Protocol
(UDP-Lite), as described in RFC\ 3828.
.PP
UDP-Lite is an extension of UDP (RFC\ 768) to support variable-length
checksums.
This has advantages for some types of multimedia transport that
may be able to make use of slightly damaged datagrams,
rather than having them discarded by lower-layer protocols.
.PP
The variable-length checksum coverage is set via a
.BR setsockopt (2)
option.
If this option is not set, the only difference from UDP is
in using a different IP protocol identifier (IANA number 136).
.PP
The UDP-Lite implementation is a full extension of
.BR udp (7)\[em]that
is, it shares the same API and API behavior, and in addition
offers two socket options to control the checksum coverage.
.SS Address format
UDP-Litev4 uses the
.I sockaddr_in
address format described in
.BR ip (7).
UDP-Litev6 uses the
.I sockaddr_in6
address format described in
.BR ipv6 (7).
.SS Socket options
To set or get a UDP-Lite socket option, call
.BR getsockopt (2)
to read or
.BR setsockopt (2)
to write the option with the option level argument set to
.BR IPPROTO_UDPLITE .
In addition, all
.B IPPROTO_UDP
socket options are valid on a UDP-Lite socket.
See
.BR udp (7)
for more information.
.PP
The following two options are specific to UDP-Lite.
.TP
.B UDPLITE_SEND_CSCOV
This option sets the sender checksum coverage and takes an
.I int
as argument, with a checksum coverage value in the range 0..2\[ha]16-1.
.IP
A value of 0 means that the entire datagram is always covered.
Values from 1\-7 are illegal (RFC\ 3828, 3.1) and are rounded up to
the minimum coverage of 8.
.IP
With regard to IPv6 jumbograms (RFC\ 2675), the UDP-Litev6 checksum
coverage is limited to the first 2\[ha]16-1 octets, as per RFC\ 3828, 3.5.
Higher values are therefore silently truncated to 2\[ha]16-1.
If in doubt, the current coverage value can always be queried using
.BR getsockopt (2).
.TP
.B UDPLITE_RECV_CSCOV
This is the receiver-side analogue and uses the same argument format
and value range as
.BR UDPLITE_SEND_CSCOV .
This option is not required to enable traffic with partial checksum
coverage.
Its function is that of a traffic filter: when enabled, it
instructs the kernel to drop all packets which have a coverage
.I less
than the specified coverage value.
.IP
When the value of
.B UDPLITE_RECV_CSCOV
exceeds the actual packet coverage, incoming packets are silently dropped,
but may generate a warning message in the system log.
.\" SO_NO_CHECK exists and is supported by UDPv4, but is
.\" commented out in socket(7), hence also commented out here
.\".PP
.\"Since UDP-Lite mandates checksums, checksumming can not be disabled
.\"via the
.\".B SO_NO_CHECK
.\"option from
.\".BR socket (7).
.SH ERRORS
All errors documented for
.BR udp (7)
may be returned.
UDP-Lite does not add further errors.
.SH FILES
.TP
.I /proc/net/snmp
Basic UDP-Litev4 statistics counters.
.TP
.I /proc/net/snmp6
Basic UDP-Litev6 statistics counters.
.SH VERSIONS
UDP-Litev4/v6 first appeared in Linux 2.6.20.
.SH BUGS
.\" FIXME . remove this section once glibc supports UDP-Lite
Where glibc support is missing, the following definitions are needed:
.PP
.in +4n
.EX
#define IPPROTO_UDPLITE     136
.\" The following two are defined in the kernel in linux/net/udplite.h
#define UDPLITE_SEND_CSCOV  10
#define UDPLITE_RECV_CSCOV  11
.EE
.in
.SH SEE ALSO
.BR ip (7),
.BR ipv6 (7),
.BR socket (7),
.BR udp (7)
.PP
RFC\ 3828 for the Lightweight User Datagram Protocol (UDP-Lite).
.PP
.I Documentation/networking/udplite.txt
in the Linux kernel source tree