third_party/lksctp-tools/man/sctp.7

.\" (C) Copyright Sridhar Samudrala IBM Corp. 2004, 2005.
.\"
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.TH SCTP  7 2005-10-25 "Linux Man Page" "Linux Programmer's Manual" 
.SH NAME
sctp \- SCTP protocol.
.SH SYNOPSIS
.nf
.B #include <sys/socket.h>
.B #include <netinet/in.h>
.B #include <netinet/sctp.h>
.sp
.B sctp_socket = socket(PF_INET, SOCK_STREAM, IPPROTO_SCTP); 
.B sctp_socket = socket(PF_INET, SOCK_SEQPACKET, IPPROTO_SCTP);
.fi
.SH 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 
.BR ip (7),
and supports both v4 and v6 versions.
.PP
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.
.PP
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.
.PP
A 
.B 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
.PP
.B     sd = socket(PF_INET, SOCK_SEQPACKET, IPPROTO_SCTP); 
.PP
A typical server in this style uses the following socket calls in sequence
to prepare an endpoint for servicing requests.
.PP
     1. socket()
     2. bind()
     3. listen()
     4. recvmsg()
     5. sendmsg()
     6. close()
.PP
A typical client uses the following calls in sequence to setup an association
with a server to request services.
.PP
     1. socket()
     2. sendmsg()
     3. recvmsg()
     4. close()
.PP
A
.B 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
.PP
.B     sd = socket(PF_INET, SOCK_STREAM, IPPROTO_SCTP); 
.PP
A typical server in one-to-one style uses the following
system call sequence to prepare an SCTP endpoint for servicing requests:
.PP
     1. socket()
     2. bind()
     3. listen()
     4. accept()
.PP
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
.PP
     5. close()
.PP
to terminate the association. A typical client uses the following system call
sequence to setup an association with a server to request services:
.PP
     1. socket()
     2. connect()
.PP
After returning from connect(), the client uses send() and recv() calls to
send out requests and receive responses from the server. The client calls
.PP
     3. close()
.PP
to terminate this association when done.
.SH "ADDRESS FORMATS"
SCTP is built on top of IP (see 
.BR ip (7)).
The address formats defined by
.BR ip (7)
apply to SCTP.  SCTP only supports point-to-point communication; broadcasting
and multicasting are not supported.
.SH SYSCTLS
These variables can be accessed by the 
.B /proc/sys/net/sctp/* 
files or with the 
.BR sysctl (2)
interface.  In addition, most IP sysctls also apply to SCTP. See
.BR ip (7). 
.TP
Please check kernel documentation for this, at Documentation/networking/ip-sysctl.txt.
.SH "STATISTICS"
These variables can be accessed by the 
.B /proc/net/sctp/* 
files. 
.TP
.B 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.
.TP
.B 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.  
.TP
.B snmp
Displays the following statistics related to SCTP states, packets and chunks. 
.TP
.TP
.B SctpCurrEstab
The number of associations for which the current state is either ESTABLISHED,
SHUTDOWN-RECEIVED or SHUTDOWN-PENDING.
.TP
.B 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.
.TP
.B 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.
.TP
.B 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.
.TP
.B 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.
.TP
.B 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.
.TP
.B SctpChecksumErrors
The number of SCTP packets received with an invalid checksum.
.TP
.B SctpOutCtrlChunks
The number of SCTP control chunks sent (retransmissions are not included).
Control chunks are those chunks different from DATA.
.TP
.B SctpOutOrderChunks
The number of SCTP ordered data chunks sent (retransmissions are not included).
.TP
.B SctpOutUnorderChunks
The number of SCTP unordered chunks(data chunks in which the U bit is set
to 1) sent (retransmissions are not included).
.TP
.B SctpInCtrlChunks
The number of SCTP control chunks received (no duplicate chunks included).
.TP
.B SctpInOrderChunks
The number of SCTP ordered data chunks received (no duplicate chunks included).
.TP
.B SctpInUnorderChunks
The number of SCTP unordered chunks(data chunks in which the U bit is set
to 1) received (no duplicate chunks included).
.TP
.B SctpFragUsrMsgs
The number of user messages that have to be fragmented because of the MTU.
.TP
.B SctpReasmUsrMsgs
The number of user messages reassembled, after conversion into DATA chunks.
.TP
.B SctpOutSCTPPacks
The number of SCTP packets sent. Retransmitted DATA chunks are included.
.TP
.B SctpInSCTPPacks
The number of SCTP packets received. Duplicates are included.
.SH "SOCKET OPTIONS"
To set or get a SCTP socket option, call
.BR getsockopt (2)
to read or
.BR setsockopt (2)
to write the option with the option level argument set to 
.BR SOL_SCTP.
.TP
.BR 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.
.TP
.B 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.
.TP
.B 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.
.TP
.B 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.
.TP
.B 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.
.TP
.B 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.
.TP
.B 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.
.TP
.B 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.
.TP
.B 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.
.TP
.B 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.
.TP
.B 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.
.TP
.B 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.
.TP
.B 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.
.TP
.B 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.
.TP
.B 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.
.TP
.B 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.
.SH AUTHORS
Sridhar Samudrala <sri@us.ibm.com>
.SH "SEE ALSO"
.BR socket (7),
.BR socket (2),
.BR ip (7),
.BR bind (2), 
.BR listen (2),
.BR accept (2),
.BR connect (2),
.BR sendmsg (2),
.BR recvmsg (2),
.BR sysctl (2),
.BR getsockopt (2),
.BR sctp_bindx (3),
.BR sctp_connectx (3),
.BR sctp_sendmsg (3),
.BR sctp_sendv (3),
.BR sctp_send (3),
.BR sctp_recvmsg (3),
.BR sctp_recvv (3),
.BR sctp_peeloff (3),
.BR sctp_getladdrs (3),
.BR sctp_getpaddrs (3),
.BR sctp_opt_info (3).
.sp
RFC2960, RFC3309 for the SCTP specification.