man7/udplite.7

   1 .\" Copyright (c) 2008 by Gerrit Renker <gerrit@erg.abdn.ac.uk>
   2 .\"
   3 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   4 .\"
   5 .\" $Id: udplite.7,v 1.12 2008/07/23 15:22:22 gerrit Exp gerrit $
   6 .\"
   7 .TH udplite 7 (date) "Linux man-pages (unreleased)"
   8 .SH NAME
   9 udplite \- Lightweight User Datagram Protocol
  10 .SH SYNOPSIS
  11 .nf
  12 .B #include <sys/socket.h>
  13 .\" FIXME . see #defines under `BUGS',
  14 .\"        when glibc supports this, add
  15 .\"        #include <netinet/udplite.h>
  16 .P
  17 .B sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDPLITE);
  18 .fi
  19 .SH DESCRIPTION
  20 This is an implementation of the Lightweight User Datagram Protocol
  21 (UDP-Lite), as described in RFC\ 3828.
  22 .P
  23 UDP-Lite is an extension of UDP (RFC\ 768) to support variable-length
  24 checksums.
  25 This has advantages for some types of multimedia transport that
  26 may be able to make use of slightly damaged datagrams,
  27 rather than having them discarded by lower-layer protocols.
  28 .P
  29 The variable-length checksum coverage is set via a
  30 .BR setsockopt (2)
  31 option.
  32 If this option is not set, the only difference from UDP is
  33 in using a different IP protocol identifier (IANA number 136).
  34 .P
  35 The UDP-Lite implementation is a full extension of
  36 .BR udp (7)\[em]that
  37 is, it shares the same API and API behavior, and in addition
  38 offers two socket options to control the checksum coverage.
  39 .SS Address format
  40 UDP-Litev4 uses the
  41 .I sockaddr_in
  42 address format described in
  43 .BR ip (7).
  44 UDP-Litev6 uses the
  45 .I sockaddr_in6
  46 address format described in
  47 .BR ipv6 (7).
  48 .SS Socket options
  49 To set or get a UDP-Lite socket option, call
  50 .BR getsockopt (2)
  51 to read or
  52 .BR setsockopt (2)
  53 to write the option with the option level argument set to
  54 .BR IPPROTO_UDPLITE .
  55 In addition, all
  56 .B IPPROTO_UDP
  57 socket options are valid on a UDP-Lite socket.
  58 See
  59 .BR udp (7)
  60 for more information.
  61 .P
  62 The following two options are specific to UDP-Lite.
  63 .TP
  64 .B UDPLITE_SEND_CSCOV
  65 This option sets the sender checksum coverage and takes an
  66 .I int
  67 as argument, with a checksum coverage value in the range 0..2\[ha]16-1.
  68 .IP
  69 A value of 0 means that the entire datagram is always covered.
  70 Values from 1\-7 are illegal (RFC\ 3828, 3.1) and are rounded up to
  71 the minimum coverage of 8.
  72 .IP
  73 With regard to IPv6 jumbograms (RFC\ 2675), the UDP-Litev6 checksum
  74 coverage is limited to the first 2\[ha]16-1 octets, as per RFC\ 3828, 3.5.
  75 Higher values are therefore silently truncated to 2\[ha]16-1.
  76 If in doubt, the current coverage value can always be queried using
  77 .BR getsockopt (2).
  78 .TP
  79 .B UDPLITE_RECV_CSCOV
  80 This is the receiver-side analogue and uses the same argument format
  81 and value range as
  82 .BR UDPLITE_SEND_CSCOV .
  83 This option is not required to enable traffic with partial checksum
  84 coverage.
  85 Its function is that of a traffic filter: when enabled, it
  86 instructs the kernel to drop all packets which have a coverage
  87 .I less
  88 than the specified coverage value.
  89 .IP
  90 When the value of
  91 .B UDPLITE_RECV_CSCOV
  92 exceeds the actual packet coverage, incoming packets are silently dropped,
  93 but may generate a warning message in the system log.
  94 .\" SO_NO_CHECK exists and is supported by UDPv4, but is
  95 .\" commented out in socket(7), hence also commented out here
  96 .\".P
  97 .\"Since UDP-Lite mandates checksums, checksumming can not be disabled
  98 .\"via the
  99 .\".B SO_NO_CHECK
 100 .\"option from
 101 .\".BR socket (7).
 102 .SH ERRORS
 103 All errors documented for
 104 .BR udp (7)
 105 may be returned.
 106 UDP-Lite does not add further errors.
 107 .SH FILES
 108 .TP
 109 .I /proc/net/snmp
 110 Basic UDP-Litev4 statistics counters.
 111 .TP
 112 .I /proc/net/snmp6
 113 Basic UDP-Litev6 statistics counters.
 114 .SH VERSIONS
 115 UDP-Litev4/v6 first appeared in Linux 2.6.20.
 116 .SH BUGS
 117 .\" FIXME . remove this section once glibc supports UDP-Lite
 118 Where glibc support is missing, the following definitions are needed:
 119 .P
 120 .in +4n
 121 .EX
 122 #define IPPROTO_UDPLITE     136
 123 .\" The following two are defined in the kernel in linux/net/udplite.h
 124 #define UDPLITE_SEND_CSCOV  10
 125 #define UDPLITE_RECV_CSCOV  11
 126 .EE
 127 .in
 128 .SH SEE ALSO
 129 .BR ip (7),
 130 .BR ipv6 (7),
 131 .BR socket (7),
 132 .BR udp (7)
 133 .P
 134 RFC\ 3828 for the Lightweight User Datagram Protocol (UDP-Lite).
 135 .P
 136 .I Documentation/networking/udplite.txt
 137 in the Linux kernel source tree