Ubuntu Manpage: sctp - SCTP protocol.

name
synopsis
description
address formats
sysctls
statistics
socket options
authors
see also

Provided by: libsctp-dev_1.0.15+dfsg-1_amd64

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.

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>