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NAME | SYNOPSIS | DESCRIPTION | ADDRESS FORMATS | SYSCTLS | STATISTICS | SOCKET OPTIONS | AUTHORS | SEE ALSO | COLOPHON |
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SCTP(7) Linux Programmer's Manual SCTP(7)
sctp - SCTP protocol.
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/sctp.h>
sctp_socket = socket(PF_INET, SOCK_STREAM, IPPROTO_SCTP);
sctp_socket = socket(PF_INET, SOCK_SEQPACKET, IPPROTO_SCTP);
This is an implementation of the SCTP protocol as defined in RFC2960
and RFC3309. It is a message oriented, reliable transport protocol
with direct support for multihoming that runs on top of ip(7), and
supports both v4 and v6 versions.
Like TCP, SCTP provides reliable, connection oriented data delivery
with congestion control. Unlike TCP, SCTP also provides message
boundary preservation, ordered and unordered message delivery, multi-
streaming and multi-homing. Detection of data corruption, loss of
data and duplication of data is achieved by using checksums and
sequence numbers. A selective retransmission mechanism is applied to
correct loss or corruption of data.
This implementation supports a mapping of SCTP into sockets API as
defined in the draft-ietf-tsvwg-sctpsocket-10.txt(Sockets API
extensions for SCTP). Two styles of interfaces are supported.
A one-to-many style interface with 1 to MANY relationship between
socket and associations where the outbound association setup is
implicit. The syntax of a one-to-many style socket() call is
sd = socket(PF_INET, SOCK_SEQPACKET, IPPROTO_SCTP);
A typical server in this style uses the following socket calls in
sequence to prepare an endpoint for servicing requests.
1. socket()
2. bind()
3. listen()
4. recvmsg()
5. sendmsg()
6. close()
A typical client uses the following calls in sequence to setup an
association with a server to request services.
1. socket()
2. sendmsg()
3. recvmsg()
4. close()
A one-to-one style interface with a 1 to 1 relationship between
socket and association which enables existing TCP applications to be
ported to SCTP with very little effort. The syntax of a one-to-one
style socket() call is
sd = socket(PF_INET, SOCK_STREAM, IPPROTO_SCTP);
A typical server in one-to-one style uses the following system call
sequence to prepare an SCTP endpoint for servicing requests:
1. socket()
2. bind()
3. listen()
4. accept()
The accept() call blocks until a new association is set up. It
returns with a new socket descriptor. The server then uses the new
socket descriptor to communicate with the client, using recv() and
send() calls to get requests and send back responses. Then it calls
5. close()
to terminate the association. A typical client uses the following
system call sequence to setup an association with a server to request
services:
1. socket()
2. connect()
After returning from connect(), the client uses send() and recv()
calls to send out requests and receive responses from the server. The
client calls
3. close()
to terminate this association when done.
SCTP is built on top of IP (see ip(7)). The address formats defined
by ip(7) apply to SCTP. SCTP only supports point-to-point
communication; broadcasting and multicasting are not supported.
These variables can be accessed by the /proc/sys/net/sctp/* files or
with the sysctl(2) interface. In addition, most IP sysctls also
apply to SCTP. See ip(7).
Please check kernel documentation for this, at
Documentation/networking/ip-sysctl.txt.
These variables can be accessed by the /proc/net/sctp/* files.
assocs Displays the following information about the active
associations. assoc ptr, sock ptr, socket style, sock state,
association state, hash bucket, association id, bytes in
transmit queue, bytes in receive queue, user id, inode, local
port, remote port, local addresses and remote addresses.
eps Displays the following information about the active endpoints.
endpoint ptr, sock ptr, socket style, sock state, hash bucket,
local port, user id, inode and local addresses.
snmp Displays the following statistics related to SCTP states,
packets and chunks.
SctpCurrEstab
The number of associations for which the current state is
either ESTABLISHED, SHUTDOWN-RECEIVED or SHUTDOWN-PENDING.
SctpActiveEstabs
The number of times that associations have made a direct
transition to the ESTABLISHED state from the COOKIE-ECHOED
state. The upper layer initiated the association attempt.
SctpPassiveEstabs
The number of times that associations have made a direct
transition to the ESTABLISHED state from the CLOSED state. The
remote endpoint initiated the association attempt.
SctpAborteds
The number of times that associations have made a direct
transition to the CLOSED state from any state using the
primitive 'ABORT'. Ungraceful termination of the association.
SctpShutdowns
The number of times that associations have made a direct
transition to the CLOSED state from either the SHUTDOWN-SENT
state or the SHUTDOWN-ACK-SENT state. Graceful termination of
the association.
SctpOutOfBlues
The number of out of the blue packets received by the host. An
out of the blue packet is an SCTP packet correctly formed,
including the proper checksum, but for which the receiver was
unable to identify an appropriate association.
SctpChecksumErrors
The number of SCTP packets received with an invalid checksum.
SctpOutCtrlChunks
The number of SCTP control chunks sent (retransmissions are
not included). Control chunks are those chunks different from
DATA.
SctpOutOrderChunks
The number of SCTP ordered data chunks sent (retransmissions
are not included).
SctpOutUnorderChunks
The number of SCTP unordered chunks(data chunks in which the U
bit is set to 1) sent (retransmissions are not included).
SctpInCtrlChunks
The number of SCTP control chunks received (no duplicate
chunks included).
SctpInOrderChunks
The number of SCTP ordered data chunks received (no duplicate
chunks included).
SctpInUnorderChunks
The number of SCTP unordered chunks(data chunks in which the U
bit is set to 1) received (no duplicate chunks included).
SctpFragUsrMsgs
The number of user messages that have to be fragmented because
of the MTU.
SctpReasmUsrMsgs
The number of user messages reassembled, after conversion into
DATA chunks.
SctpOutSCTPPacks
The number of SCTP packets sent. Retransmitted DATA chunks are
included.
SctpInSCTPPacks
The number of SCTP packets received. Duplicates are included.
To set or get a SCTP socket option, call getsockopt(2) to read or
setsockopt(2) to write the option with the option level argument set
to SOL_SCTP.
SCTP_RTOINFO.
This option is used to get or set the protocol parameters used
to initialize and bound retransmission timout(RTO). The
structure sctp_rtoinfo defined in /usr/include/netinet/sctp.h
is used to access and modify these parameters.
SCTP_ASSOCINFO
This option is used to both examine and set various
association and endpoint parameters. The sturcture
sctp_assocparams defined in /usr/include/netinet/sctp.h is
used to access and modify these parameters.
SCTP_INITMSG
This option is used to get or set the protocol parameters for
the default association initialization. The structure
sctp_initmsg defined in /usr/include/netinet/sctp.h is used to
access and modify these parameters.
Setting initialization parameters is effective only on an
unconnected socket (for one-to-many style sockets only future
associations are effected by the change). With one-to-one
style sockets, this option is inherited by sockets derived
from a listener socket.
SCTP_NODELAY
Turn on/off any Nagle-like algorithm. This means that packets
are generally sent as soon as possible and no unnecessary
delays are introduced, at the cost of more packets in the
network. Expects an integer boolean flag.
SCTP_AUTOCLOSE
This socket option is applicable to the one-to-many style
socket only. When set it will cause associations that are idle
for more than the specified number of seconds to automatically
close. An association being idle is defined an association
that has NOT sent or received user data. The special value of
0 indicates that no automatic close of any associations should
be performed. The option expects an integer defining the
number of seconds of idle time before an association is
closed.
SCTP_SET_PEER_PRIMARY_ADDR
Requests that the peer mark the enclosed address as the
association primary. The enclosed address must be one of the
association's locally bound addresses. The structure
sctp_setpeerprim defined in /usr/include/netinet/sctp.h is
used to make a set peer primary request.
SCTP_PRIMARY_ADDR
Requests that the local SCTP stack use the enclosed peer
address as the association primary. The enclosed address must
be one of the association peer's addresses. The structure
sctp_prim defined in /usr/include/netinet/sctp.h is used to
make a get/set primary request.
SCTP_DISABLE_FRAGMENTS
This option is a on/off flag and is passed an integer where a
non-zero is on and a zero is off. If enabled no SCTP message
fragmentation will be performed. Instead if a message being
sent exceeds the current PMTU size, the message will NOT be
sent and an error will be indicated to the user.
SCTP_PEER_ADDR_PARAMS
Using this option, applications can enable or disable
heartbeats for any peer address of an association, modify an
address's heartbeat interval, force a heartbeat to be sent
immediately, and adjust the address's maximum number of
retransmissions sent before an address is considered
unreachable. The structure sctp_paddrparams defined in
/usr/include/netinet/sctp.h is used to access and modify an
address's parameters.
SCTP_DEFAULT_SEND_PARAM
Applications that wish to use the sendto() system call may
wish to specify a default set of parameters that would
normally be supplied through the inclusion of ancillary data.
This socket option allows such an application to set the
default sctp_sndrcvinfo structure. The application that wishes
to use this socket option simply passes in to this call the
sctp_sndrcvinfo structure defined in
/usr/include/netinet/sctp.h. The input parameters accepted by
this call include sinfo_stream, sinfo_flags, sinfo_ppid,
sinfo_context, sinfo_timetolive. The user must set the
sinfo_assoc_id field to identify the
association to affect if the caller is using the one-to-many
style.
SCTP_EVENTS
This socket option is used to specify various notifications
and ancillary data the user wishes to receive. The structure
sctp_event_subscribe defined in /usr/include/netinet/sctp.h is
used to access or modify the events of interest to the user.
SCTP_I_WANT_MAPPED_V4_ADDR
This socket option is a boolean flag which turns on or off
mapped V4 addresses. If this option is turned on and the
socket is type PF_INET6, then IPv4 addresses will be mapped to
V6 representation. If this option is turned off, then no
mapping will be done of V4 addresses and a user will receive
both PF_INET6 and PF_INET type addresses on the socket.
By default this option is turned on and expects an integer to
be passed where non-zero turns on the option and zero turns
off the option.
SCTP_MAXSEG
This socket option specifies the maximum size to put in any
outgoing SCTP DATA chunk. If a message is larger than this
size it will be fragmented by SCTP into the specified size.
Note that the underlying SCTP implementation may fragment into
smaller sized chunks when the PMTU of the underlying
association is smaller than the value set by the user. The
option expects an integer.
The default value for this option is 0 which indicates the
user is NOT limiting fragmentation and only the PMTU will
effect SCTP's choice of DATA chunk size.
SCTP_STATUS
Applications can retrieve current status information about an
association, including association state, peer receiver window
size, number of unacked data chunks, and number of data chunks
pending receipt. This information is read-only. The
structure sctp_status defined in /usr/include/netinet/sctp.h
is used to access this information.
SCTP_GET_PEER_ADDR_INFO
Applications can retrieve information about a specific peer
address of an association, including its reachability state,
congestion window, and retransmission timer values. This
information is read-only. The structure sctp_paddr_info
defined in /usr/include/netinet/sctp.h is used to access this
information.
SCTP_GET_ASSOC_STATS
Applications can retrieve current statistics about an
association, including SACKs sent and received, SCTP packets
sent and received. The complete list can be found in
/usr/include/netinet/sctp.h in struct sctp_assoc_stats.
Sridhar Samudrala <sri@us.ibm.com>
socket(7), socket(2), ip(7), bind(2), listen(2), accept(2),
connect(2), sendmsg(2), recvmsg(2), sysctl(2), getsockopt(2),
sctp_bindx(3), sctp_connectx(3), sctp_sendmsg(3), sctp_send(3),
sctp_recvmsg(3), sctp_peeloff(3), sctp_getladdrs(3),
sctp_getpaddrs(3), sctp_opt_info(3).
RFC2960, RFC3309 for the SCTP specification.
This page is part of the lksctp-tools (Linux kernel SCTP tools)
project. Information about the project can be found at
⟨http://lksctp.org/⟩. If you have a bug report for this manual page,
send it to sctp@vger.kernel.org. This page was obtained from the
project's upstream Git repository
⟨git://github.com/sctp/lksctp-tools.git⟩ on 2018-02-02. (At that
time, the date of the most recent commit that was found in the repos‐
itory was 2017-12-01.) If you discover any rendering problems in
this HTML version of the page, or you believe there is a better or
more up-to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not part
of the original manual page), send a mail to man-pages@man7.org
Linux Man Page 2005-10-25 SCTP(7)
Pages that refer to this page: sctp_bindx(3), sctp_connectx(3), sctp_getladdrs(3), sctp_getpaddrs(3), sctp_opt_info(3), sctp_peeloff(3), sctp_recvmsg(3), sctp_send(3), sctp_sendmsg(3)
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