This is an implementation of the Lightweight User Datagram Protocol
(UDP-Lite), as described in RFC 3828.
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.
The variable-length checksum coverage is set via a
setsockopt(2)
option.
If this option is not set, the only difference to UDP is
in using a different IP protocol identifier (IANA number 136).
The UDP-Lite implementation is a full extension of
udp(7),
i.e., it shares the same API and API behaviour, and in addition
offers two socket options to control the checksum coverage.
Address Format
UDP-Litev4 uses the
sockaddr_in
address format described in
ip(7).
UDP-Litev6 uses the
sockaddr_in6
address format described in
ipv6(7).
Socket Options
To set or get a UDP-Lite socket option, call
getsockopt(2)
to read or
setsockopt(2)
to write the option with the option level argument set to
IPPROTO_UDPLITE.
In addition, all
IPPROTO_UDP
socket options are valid on a UDP-Lite socket.
See
udp(7)
for more information.
The following two options are specific to UDP-Lite.
UDPLITE_SEND_CSCOV
This option sets the sender checksum coverage and takes an
int
as argument, with a checksum coverage value in the range 0..2^16-1.
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.
With regard to IPv6 jumbograms (RFC 2675), the UDP-Litev6 checksum
coverage is limited to the first 2^16-1 octets, as per RFC 3828, 3.5.
Higher values are therefore silently truncated to 2^16-1.
If in doubt, the current coverage value can always be queried using
getsockopt(2).
UDPLITE_RECV_CSCOV
This is the receiver-side analogue and uses the same argument format
and value range as
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
less
than the specified coverage value.
When the value of
UDPLITE_RECV_CSCOV
exceeds the actual packet coverage, incoming packets are silently dropped,
but may generate a warning message in the system log.
ERRORS
All errors documented for
udp(7)
may be returned.
UDP-Lite does not add further errors.
BUGS
Where glibc support is missing, the following definitions are needed:
RFC 3828 for the Lightweight User Datagram Protocol (UDP-Lite)
Documentation/networking/udplite.txt
COLOPHON
This page is part of release 3.14 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
