sctp(7) — Linux manual page

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 timeout(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 structure
              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_paddrinfo 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_sendv(3),
       sctp_send(3), sctp_recvmsg(3), sctp_recvv(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 [unknown
       -- if you know, please contact man-pages@man7.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
       ⟨https://github.com/sctp/lksctp-tools.git⟩ on 2021-04-01.  (At
       that time, the date of the most recent commit that was found in
       the repository was 2021-01-11.)  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_recvv(3)sctp_send(3)sctp_sendmsg(3)sctp_sendv(3)ip(7)