Provided by: libsctp-dev_1.0.19+dfsg-2_amd64 bug

NAME

       sctp - SCTP protocol.

SYNOPSIS

       #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

       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

       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

       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

       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

       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

       Sridhar Samudrala <sri@us.ibm.com>

SEE ALSO

       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.