NAME | SYNOPSIS | DESCRIPTION | ADDRESS FORMATS | SYSCTLS | STATISTICS | SOCKET OPTIONS | AUTHORS | SEE ALSO | COLOPHON

SCTP(7)                   Linux Programmer's Manual                  SCTP(7)

NAME         top

       sctp - SCTP protocol.

SYNOPSIS         top

       #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);

DESCRIPTION         top

       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.

ADDRESS FORMATS         top

       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.

SYSCTLS         top

       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.

STATISTICS         top

       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.

SOCKET OPTIONS         top

       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.

AUTHORS         top

       Sridhar Samudrala <sri@us.ibm.com>

SEE ALSO         top

       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.

COLOPHON         top

       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 2017-11-25.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2017-09-27.)  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)