Provided by: libsctp-dev_1.0.11+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).

       addip_enable
              Enable SCTP ADDIP(Dynamic Address Reconfiguration) Support. This is off by default.

       association_max_retrans
              Maximum number  of  consecutive  retransmissions  to  a  peer  before  an  endpoint
              considers  that  the  peer  is  unreachable and closes the association. The default
              value is 10.

       cookie_preserve_enable
              Handle COOKIE PRESERVATIVE parameter in the INIT chunk. This is on by default.

       hb_interval
              This is the interval when a HEARTBEAT chunk is  sent  to  a  destination  transport
              address  to monitor the reachability of an idle destination transport address.  The
              default is 30 seconds and is maintained in msecs.

       max_burst
              Maximum number of new data packets that can be sent in a burst. The  default  value
              is 4.

       max_init_retransmits
              Maximum  number  of  times  an  INIT  chunk or a COOKIE ECHO chunk is retransmitted
              before an endpoint aborts the initialization process and  closes  the  association.
              The default value is 8.

       path_max_retrans
              Maximum  number of consecutive retransmissions over a destination transport address
              of a peer endpoint before it is marked as inactive. The default value is 5.

       prsctp_enable
              Enable PR-SCTP. This is on by default.

       rcvbuf_policy
              This controls the socket receive buffer accounting policy. The default value  is  0
              and  indicates  that  all  the  associations  belonging  to a socket share the same
              receive buffer space. When set to 1, each association will  have  its  own  receive
              buffer space.

       rto_alpha_exp_divisor
              This  is  the  RTO.Alpha  value  when  expressed in right shifts and is used in RTO
              calculations. The default value is 3.

       rto_beta_exp_divisor
              This is the RTO.Beta value when expressed in  right  shifts  and  is  used  in  RTO
              calculations. The default value is 2.

       rto_initial
              This  is  the  initial  value  of  RTO(retransmission  timeout) that is used in RTO
              calculations. The default value is 3 seconds and is maintained in msecs.

       rto_max
              This is the maximum value of  RTO(retransmission  timeout)  that  is  used  in  RTO
              calculations. The default value is 60 seconds and is maintained in msecs.

       rto_min
              This  is  the  minimum  value  of  RTO(retransmission  timeout) that is used in RTO
              calculations. The default value is 1 second and is maintained in msecs.

       sack_timeout
              Delayed SACK timeout. The default value is 200msecs.

       sndbuf_policy
              This controls the socket sendbuffer accounting policy. The default value is  0  and
              indicates  that  all  the  associations  belonging  to a socket share the same send
              buffer space. When set to 1, each association will have its own send buffer space.

       valid_cookie_life
              This is the maximum lifespan of the Cookie sent in an INIT ACK chunk.  The  default
              value is 60 secs and is maintained in msecs.

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  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.

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_send(3),  sctp_recvmsg(3),  sctp_peeloff(3),  sctp_getladdrs(3),   sctp_getpaddrs(3),
       sctp_opt_info(3).

       RFC2960, RFC3309 for the SCTP specification.