SCTP(7)

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 RFC4960. 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 RFC6458(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.rst.

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, remote addresses, heartbeat interval, in streams, out streams, max retransmissions, init retries, shutdown retries, retransmitted chunks, sock transmit queue committed bytes, sock transmit queue bytes, and sock send and receive buffer bytes.

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.

SctpT1InitExpireds
    The number of timer T1 INIT expired.

SctpT1CookieExpireds
    The number of timer T1 COOKIE-ECHO expired.

SctpT2ShutdownExpireds
    The number of timer T2 SHUTDOWN expired.

SctpT3RtxExpireds
    The number of timer T3 RTX expired.

SctpT4RtoExpireds
    The number of timer T4 RTO expired.

SctpT5ShutdownGuardExpireds
    The number of timer T5 SHUTDOWN GUARD expired.

SctpDelaySackExpireds
    The number of timer DELAY_SACK expired.

SctpAutocloseExpireds
    The number of timer AUTOCLOSE expired.

SctpT3Retransmits
    The number of T3 timer retransmission.

SctpPmtudRetransmits
    The number of PMTUD retransmission.

SctpFastRetransmits
    The number of FAST retransmission.

SctpInPktSoftirq
    The number of SCTP packets received in Softirq.

SctpInPktBacklog
    The number of SCTP packets received in Backlog.

SctpInPktDiscards
    The number of SCTP packets discarded in receiving.

SctpInDataChunkDiscards
    The number of SCTP data chunks discarded in receiving.

CONTROL MSGS
The ancillary data is carried in msg_control field of struct msghdr, which is used in sendmsg(2) and recvmsg(2) call. The SCTP stack uses the ancillary data to communicate the attributes, such as SCTP_RCVINFO, of the message stored in msg_iov to the socket endpoint. Each ancillary data item is preceded by a struct cmsghdr, see cmsg(3). The different cmsg types for SCTP are listed below, and all these related macros and structures are defined in /usr/include/netinet/sctp.h.

SCTP_INIT
    This cmsg provides information for initializing new SCTP associations for sendmsg() with struct sctp_initmsg, which is the same as SCTP_INITMSG socket option's data structure.

SCTP_SNDRCV
    This cmsg specifies SCTP options for sendmsg() and describes SCTP header information about a received message through recvmsg() with struct sctp_sndrcvinfo. It mixes the send and receive path, and SCTP_SNDINFO and SCTP_RCVINFO split this information, so these structures should be used, when possible, since SCTP_SNDRCV is deprecated. sctp_sendmsg(3) and sctp_send(3) provide a simple way to use this cmsg. Note that an application must use the SCTP_RECVRCVINFO socket option to enable the delivery of this information.

SCTP_EXTRCV
    This cmsg specifies SCTP options for SCTP header information about a received message via recvmsg() with struct sctp_extrcvinfo, and this structure is an extended version of SCTP_SNDRCV. Note that data in the next message is not valid unless the current message is completely read, i.e., unless the MSG_EOR is set. SCTP_NXTINFO should be used when possible, since SCTP_EXTRCV is considered deprecated. sctp_recvmsg(3) provides a simple way to use this cmsg. Note that an application must use the SCTP_RECVNXTINFO socket option to enable the delivery of this information.

SCTP_RCVINFO, SCTP_NXTINFO
    These cmsgs describe SCTP receive information about a received message through recvmsg() with struct sctp_rcvinfo, and SCTP receive information of the next message that will be delivered through recvmsg() if this information is already available when delivering the current message with struct sctp_nxtinfo. sctp_recvv(3) provides a simple way to use these cmsgs. Note that an application must use the SCTP_RECVRCVINFO and SCTP_RECVNXTINFO socket options accordingly to enable the delivery of this information.

SCTP_SNDINFO, SCTP_PRINFO, SCTP_AUTHINFO, SCTP_DSTADDRV4, SCTP_DSTADDRV6
    These cmsgs specifie a couple of SCTP options for sendmsg() for SEND, PRSCTP, AUTH and DSTADDR information with struct sctp_sndinfo, sctp_prinfo, sctp_authinfo and in(6)_addr accordingly. sctp_sendv(3) provides a simple way to use these cmsgs.

EVENTS and NOTIFICATIONS
An SCTP application may need to understand and process events and errors that happen on the SCTP stack. These events include network status changes, association startups, remote operational errors, and undeliverable messages. When a notification arrives, recvmsg() returns the notification in the application-supplied data buffer via msg_iov, and sets MSG_NOTIFICATION in msg_flags. See socket option SCTP_EVENT for the event enabling. The different events are listed below, and all these related macros and structures are defined in /usr/include/netinet/sctp.h.

SCTP_ASSOC_CHANGE
    Communication notifications inform the application that an SCTP association has either begun or ended. The notification format is struct sctp_assoc_change.

SCTP_PEER_ADDR_CHANGE
    When a destination address of a multi-homed peer encounters a state change, a peer address change event is sent. The notification format is struct sctp_paddr_change.

SCTP_REMOTE_ERROR
    A remote peer may send an Operation Error message to its peer. This message indicates a variety of error conditions on an association. The notification format is struct sctp_remote_error.

SCTP_SEND_FAILED
    If SCTP cannot deliver a message, it can return back the message as a notification if the SCTP_SEND_FAILED event is enabled. The notification format is struct sctp_send_failed. Please note that this notification is deprecated. Use SCTP_SEND_FAILED_EVENT instead.

SCTP_SHUTDOWN_EVENT
    When a peer sends a SHUTDOWN, SCTP delivers this notification to inform the application that it should cease sending data. The notification format is struct sctp_shutdown_event.

SCTP_ADAPTATION_INDICATION
    When a peer sends an Adaptation Layer Indication parameter, SCTP delivers this notification to inform the application about the peer's adaptation layer indication. The notification format is struct sctp_adaptation_event.

SCTP_PARTIAL_DELIVERY_EVENT
    When a receiver is engaged in a partial delivery of a message, this notification will be used to indicate various events. The notification format is struct sctp_pdapi_event.

SCTP_AUTHENTICATION_EVENT
    This is used to report different events relating to the use of the extension to authenticate SCTP messages. The notification format is struct sctp_authkey_event.

SCTP_SENDER_DRY_EVENT
    When the SCTP stack has no more user data to send or retransmit, this notification is given to the user. Also, at the time when a user app subscribes to this event, if there is no data to be sent or retransmit, the stack will immediately send up this notification. The notification format is struct sctp_sender_dry_event.

SCTP_SEND_FAILED_EVENT
    If SCTP cannot deliver a message, it can return back the message as a notification if the SCTP_SEND_FAILED_EVENT event is enabled. The notification format is struct sctp_send_failed_event.

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. Note that all these macros and structures described for parameters are defined in /usr/include/netinet/sctp.h, and for one-to-one style sockets a specified assoc_id works the same as SCTP_FUTURE_ASSOC.

SCTP_RTOINFO.
    This option is used to get or set the protocol parameters used to initialize and bound retransmission timeout(RTO). The parameter type is struct sctp_rtoinfo, for reading and writing. srto_assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC. Default: srto_max=sysctl_net.sctp.rto_max, srto_min=sysctl_net.sctp.rto_min, srto_initial=sysctl_net.sctp.rto_initial.

SCTP_ASSOCINFO
    This option is used to both examine and set various association and endpoint parameters. The parameter type is struct sctp_assocparams, for reading and writing. sasoc_assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC. Note that some fields of this structure are for reading only:
      struct sctp_assocparams {
              sctp_assoc_t sasoc_assoc_id;
              __u16 sasoc_asocmaxrxt; (RW)
              __u16 sasoc_number_peer_destinations; (R)
              __u32 sasoc_peer_rwnd; (R)
              __u32 sasoc_local_rwnd; (R)
              __u32 sasoc_cookie_life; (RW)
      }; Default: sasoc_asocmaxrxt=sysctl_net.sctp.association_max_retrans, sasoc_cookie_life=sysctl_net.sctp.valid_cookie_life.

SCTP_INITMSG
    This option is used to get or set the protocol parameters for the default association initialization. The parameter type is struct sctp_initmsg, for reading and writing. Default: sinit_num_ostreams=10, sinit_max_instreams=10, sinit_max_attempts=sysctl_net.sctp.max_init_retransmits, sinit_max_init_timeo=sysctl_net.sctp.rto_max.

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. The parameter type is int boolean, for reading and writing. Default: 0.

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 within a period. The parameter type is int(seconds), for reading and writing. 0 indicates that no automatic close of any associations should be performed. Default: sysctl_net.sctp.max_autoclose.

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 parameter type is struct sctp_setpeerprim, for writing only. sspp_assoc_id is a specified assoc_id. Default: the 1st local address added. Require: SCTP_ASCONF_SUPPORTED.

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 parameter type is struct sctp_prim, for writing only. ssp_assoc_id is a specified assoc_id. Default: the 1st peer address added. Require: SCTP_ASCONF_SUPPORTED.

SCTP_DISABLE_FRAGMENTS
    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. The parameter type is int boolean, for reading and writing. Default: 0.

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 parameter type is struct sctp_paddrparams, for reading and writing. spp_address is a specified transport address or 0, spp_assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC. Default: hbinterval=sysctl_net.sctp.hb_interval, pathmaxrxt=sysctl_net.sctp.path_max_retrans, pathmtu=dev/route's, sackdelay=sysctl_net.sctp.sack_timeout, param_flags=HB_ENABLE|PMTUD_ENABLE|SACKDELAY_ENABLE, flowlabel=0, dscp=0.

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 option has been obsoleted by SCTP_DEFAULT_SNDINFO. The parameter type is struct sctp_sndrcvinfo. For reading, sinfo_assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC. For writing, sinfo_assoc_id is a specified assoc_id or SCTP_{FUTURE|CURRENT|ALL}_ASSOC. Default: default_stream=0, default_flags=0, default_ppid=0, default_context=0, default_timetolive=0.

SCTP_EVENTS
    This socket option is used to specify various notifications and ancillary data the user wishes to receive. This option has been obsoleted by SCTP_EVENT. The parameter type is struct sctp_event_subscribe, for reading and writing. Default: 0.

SCTP_I_WANT_MAPPED_V4_ADDR
    This socket option is used to turn 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. The parameter type is int boolean, for reading and writing. Default: 1.

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. 0 indicates the user is NOT limiting fragmentation and only the PMTU will effect SCTP's choice of DATA chunk size. The parameter type is struct sctp_assoc_value, for reading and writing. assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC. Default: 0(no limit).

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. The parameter type is struct sctp_status, for reading only. sstat_assoc_id is a specified assoc_id.

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. The parameter type is struct sctp_paddrinfo, for reading only. spinfo_address is a specified transport address, sas_assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC.

SCTP_GET_ASSOC_STATS
    Applications can retrieve current statistics about an association, including SACKs sent and received, SCTP packets sent and received. The parameter type is struct sctp_assoc_stats, for reading only. sas_assoc_id is a specified assoc_id.

SCTP_DELAYED_ACK, SCTP_DELAYED_ACK_TIME, SCTP_DELAYED_SACK
    These options will affect the way delayed SACKs are performed. They allow the application to get or set the delayed SACK time, in milliseconds, and also allow changing the delayed SACK frequency. Changing the frequency to 1 disables the delayed SACK algorithm. Note that if sack_delay or sack_freq is 0 when setting this option, the current values will remain unchanged. The parameter type is struct sctp_sack_info. For reading, sack_assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC. For writing, sack_assoc_id is a specified assoc_id or SCTP_{FUTURE|CURRENT|ALL}_ASSOC. Default: sackdelay=sysctl_net.sctp.sack_timeout,sackfreq=2.

SCTP_CONTEXT
    This option allows the setting, on an association basis, of a default context that will be received on reading messages from the peer. This is especially helpful for an application when using one-to-many style sockets to keep some reference to an internal state machine that is processing messages on the association. Note that the setting of this value only affects received messages from the peer and does not affect the value that is saved with outbound messages. The parameter type is struct sctp_assoc_value. For reading, assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC. For writing, assoc_id is a specified assoc_id or SCTP_{FUTURE|CURRENT|ALL}_ASSOC. Default: 0.

SCTP_FRAGMENT_INTERLEAVE
    Fragmented interleave controls how the presentation of messages occurs for the message receiver. There are three levels of fragment interleave defined: level 0: SCTP_FRAGMENT_INTERLEAVE = 0; level 1: SCTP_FRAGMENT_INTERLEAVE = 1; level 2: SCTP_FRAGMENT_INTERLEAVE = 1 & SCTP_INTERLEAVING_SUPPORTED = 1. The parameter type is int boolean, for reading and writing. Default: 0.

SCTP_PARTIAL_DELIVERY_POINT
    This option will set or get the SCTP partial delivery point. This point is the size of a message where the partial delivery API will be invoked to help free up rwnd space for the peer. Setting this to a lower value will cause partial deliveries to happen more often. This option expects an integer that sets or gets the partial delivery point in bytes. Note also that the call will fail if the user attempts to set this value larger than the socket receive buffer size. Note that any single message having a length smaller than or equal to the SCTP partial delivery point will be delivered in a single read call as long as the user-provided buffer is large enough to hold the message. The parameter type is uint32_t, for reading and writing. Default: 0.

SCTP_MAX_BURST
    This option will allow a user to change the maximum burst of packets that can be emitted by this association. The parameter type is struct sctp_assoc_value. For reading, assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC. For writing, assoc_id is a specified assoc_id or SCTP_{FUTURE|CURRENT|ALL}_ASSOC. Default: sysctl_net.sctp.max_burst.

SCTP_AUTH_CHUNK
    This option adds a chunk type that the user is requesting to be received only in an authenticated way, and it only affects the future associations. The parameter type is struct sauth_chunk, for writing only. Default: no chunks. Require: SCTP_AUTH_SUPPORTED. RFC: RFC4895.

SCTP_HMAC_IDENT
    This option gets or sets the list of Hashed Message Authentication Code (HMAC) algorithms that the local endpoint requires the peer to use. The parameter type is struct sctp_hmacalgo, for reading and writing. shmac_idents can include SCTP_AUTH_HMAC_ID_{SHA1|SHA256}. Default: SCTP_AUTH_HMAC_ID_SHA1. Require: SCTP_AUTH_SUPPORTED.

SCTP_AUTH_KEY
    This option will set a shared secret key that is used to build an association shared key. The parameter type is struct sctp_authkey, for writing only. sca_assoc_id is a specified assoc_id or SCTP_{FUTURE|CURRENT|ALL}_ASSOC. Default: null_key. Require: SCTP_AUTH_SUPPORTED.

SCTP_AUTH_ACTIVE_KEY
    This option will get or set the active shared key to be used to build the association shared key. The parameter type is struct sctp_authkeyid, for writing only. scact_assoc_id is a specified assoc_id or SCTP_{FUTURE|CURRENT|ALL}_ASSOC. Default: 0. Require: SCTP_AUTH_SUPPORTED.

SCTP_AUTH_DEACTIVATE_KEY
    This set option indicates that the application will no longer send user messages using the indicated key identifier. The parameter type is struct sctp_authkeyid, for writing only. scact_assoc_id is a specified assoc_id or SCTP_{FUTURE|CURRENT|ALL}_ASSOC. Require: SCTP_AUTH_SUPPORTED.

SCTP_AUTH_DELETE_KEY
    This set option will delete an SCTP association's shared secret key that has been deactivated. The parameter type is struct sctp_authkeyid, for writing only. scact_assoc_id is a specified assoc_id or SCTP_{FUTURE|CURRENT|ALL}_ASSOC. Require: SCTP_AUTH_SUPPORTED.

SCTP_PEER_AUTH_CHUNKS
    This option gets a list of chunk types for a specified association that the peer requires to be received authenticated only. The parameter type is struct sctp_authchunks, for reading only. gauth_assoc_id is a specified assoc_id. Require: SCTP_AUTH_SUPPORTED.

SCTP_LOCAL_AUTH_CHUNKS
    This option gets a list of chunk types for a specified association that the local endpoint requires to be received authenticated only. The parameter type is struct sctp_authchunks, for reading only. gauth_assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC. Require: SCTP_AUTH_SUPPORTED.

SCTP_GET_ASSOC_NUMBER
    This option gets the current number of associations that are attached to a one-to-many style socket. Note that this number is only a snapshot. This means that the number of associations may have changed when the caller gets back the option result. The parameter type is uint32_t, for reading only.

SCTP_GET_ASSOC_ID_LIST
    This option gets the current list of SCTP association identifiers of the SCTP associations handled by a one-to-many style socket. It uses struct sctp_assoc_ids and must provide a large enough buffer to hold all association identifiers. If the buffer is too small, an error must be returned. The user can use the SCTP_GET_ASSOC_NUMBER socket option to get an idea of how large the buffer has to be. The parameter type is struct sctp_assoc_ids, for reading only.

SCTP_EXPOSE_POTENTIALLY_FAILED_STATE, SCTP_EXPOSE_PF_STATE
    Applications can control the exposure of the PF path state in the SCTP_PEER_ADDR_CHANGE event, and if pf_expose is not 'enabled', no notification will be sent for a transport state change to SCTP_PF. It also affects the SCTP_GET_PEER_ADDR_INFO socket option, and if pf_expose is 'disabled', users can not access the transport info via SCTP_GET_PEER_ADDR_INFO option. The parameter type is struct sctp_assoc_value, for reading and writing. assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC. Default: sysctl_net.sctp.pf_expose.

SCTP_PEER_ADDR_THLDS
    Applications can control the SCTP-PF behavior by getting or setting the number of consecutive timeouts before a peer address is considered PF or unreachable.. The parameter type is struct sctp_paddrthlds, for reading and writing. spt_address is a specified transport address or 0, spt_assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC. Default: pathmaxrxt=sysctl_net.sctp.path_max_retrans, ps_retrans=sysctl_net.sctp.ps_retrans.

SCTP_PEER_ADDR_THLDS_V2
    Similar to SCTP_PEER_ADDR_THLDS, but it can also be used by applications to set and get the number of timeouts before the primary path is changed automatically by the Primary Path Switchover function. The parameter type is struct sctp_paddrthlds_v2, for reading and writing. spt_address is a specified transport address or 0, spt_assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC. Default: pathmaxrxt=sysctl_net.sctp.path_max_retrans, ps_retrans=sysctl_net.sctp.ps_retrans, pf_retrans=sysctl_net.sctp.pf_retrans.

SCTP_RECVRCVINFO
    Setting this option specifies that SCTP_RCVINFO (SCTP receive information about a received message) is returned as ancillary data by recvmsg(). See CONTROL MSGS for more details. The parameter type is int, for reading and writing. Default: 0.

SCTP_RECVNXTINFO
    Setting this option specifies that SCTP_NXTINFO (SCTP receive information of the next message) is returned as ancillary data by recvmsg(). See CONTROL MSGS for details. The parameter type is int, for reading and writing. Default: 0.

SCTP_DEFAULT_SNDINFO
    This option obsoletes SCTP_DEFAULT_SEND_PARAM. The parameter type is struct sctp_sndinfo. For reading, snd_assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC. For writing, snd_assoc_id is a specified assoc_id or SCTP_{FUTURE|CURRENT|ALL}_ASSOC. Default: default_stream=0, default_flags=0, default_ppid=0, default_context=0.

SCTP_REUSE_PORT
    This option is similar to the socket level option SO_REUSEADDR, besides only supports one-to-one style SCTP sockets and must not be used after calling bind() or sctp_bindx(). The parameter type is int, for reading and writing. Default: 0.

SCTP_SOCKOPT_BINDX_ADD
    This option allows the user to bind a specific subset of addresses or, if the SCTP extension ASCONF is supported (see SCTP_ASCONF_SUPPORTED), add specific addresses. The API sctp_bindx() is based on this. The parameter type is struct sockaddr[], for writing only.

SCTP_SOCKOPT_BINDX_REM
    Similar to SCTP_SOCKOPT_BINDX_ADD, but delete specific addresses. The API sctp_bindx() is based on this. The parameter type is struct sockaddr[], for writing only.

SCTP_SOCKOPT_PEELOFF
    This option branches off an UDP type association into a separate socket returned back to users. The API sctp_peeloff() is based on this option. The parameter type is sctp_peeloff_arg_t, for reading only. associd is a specified assoc_id.

SCTP_SOCKOPT_PEELOFF_FLAGS
    Peel off an UDP type association from a socket similar to SCTP_SOCKOPT_PEELOFF option, but it allows the flags like O_CLOEXEC and O_NONBLOCK to be used when creating the new socket. The API sctp_peeloff_flags() is based on this option. The parameter type is sctp_peeloff_flags_arg_t, for reading only. associd is a specified assoc_id.

SCTP_SOCKOPT_CONNECTX_OLD
    This option allows a user to specify multiple addresses at which a peer can be reached, and the kernel stack will use the list of addresses to set up the association. The API sctp_connectx() is based on this option. The parameter type is struct sockaddr[], for writing only.

SCTP_SOCKOPT_CONNECTX
    Similar to SCTP_SOCKOPT_CONNECTX_OLD, but it returns the new assoc's id. The API sctp_connectx2() is based on this option. The parameter type is struct sockaddr[], for writing only. The new assoc's id is passed to users by the return value.

SCTP_SOCKOPT_CONNECTX3
    Similar to SCTP_SOCKOPT_CONNECTX, but it uses different type parameter. The API sctp_connectx3() is based on this option. The parameter type is struct sctp_getaddrs_old, for reading only. assoc_id is set to the new assoc's id by kernel and passed to users.

SCTP_GET_PEER_ADDRS
    This option is used to gets all peer addresses in an association. The API sctp_getpaddrs() is based on this option. The parameter type is struct sctp_getaddrs, for reading only. assoc_id is a specified assoc_id.

SCTP_GET_LOCAL_ADDRS
    This option is used to get all local addresses in an association. The API sctp_getladdrs() is based on this option. The parameter type is struct sctp_getaddrs, for reading only. assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC.

SCTP_ADAPTATION_LAYER
    This option requests that the local endpoint set the specified Adaptation Layer Indication parameter for all future INIT and INIT-ACK exchanges. The parameter type is struct sctp_setadaptation, for reading and writing. Default: 0.

SCTP_EVENT
    This option obsoletes SCTP_EVENTS socket option, and it can set or get one specific type of event for a specified association. The parameter type is struct sctp_event. For reading, se_assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC. For writing, se_assoc_id is a specified assoc_id or SCTP_{FUTURE|CURRENT|ALL}_ASSOC. se_type can be one of enum sctp_sn_type. Default: 0.

SCTP_PR_SUPPORTED
    This socket option allows the enabling or disabling of the negotiation of PR-SCTP support for future associations. The parameter type is struct sctp_assoc_value. For reading, assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC. For writing, assoc_id is SCTP_FUTURE_ASSOC. Default: sysctl_net.sctp.prsctp_enable. RFC: RFC7496.

SCTP_DEFAULT_PRINFO
    This option sets and gets the default parameters for PR-SCTP. The parameter type is struct sctp_default_prinfo. For reading, pr_assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC. For writing, pr_assoc_id is a specified assoc_id or SCTP_{FUTURE|CURRENT|ALL}_ASSOC. pr_policy can be SCTP_PR_SCTP_{NONE|TTL|RTX|PRIO}. Default: SCTP_PR_SCTP_NONE. Require: SCTP_DEFAULT_PRINFO.

SCTP_PR_ASSOC_STATUS
    This option is used to get Association-Specific PR-SCTP Status. The parameter type is struct sctp_prstatus, for reading only. sprstat_assoc_id is a specified assoc_id, sprstat_policy can be SCTP_PR_SCTP_{TTL|RTX|PRIO|ALL}.

SCTP_PR_STREAM_STATUS
    This option is used to get Stream-Specific PR-SCTP Status. The parameter type is struct sctp_prstatus, for reading only. sprstat_assoc_id is a specified assoc_id, sprstat_policy can be SCTP_PR_SCTP_{TTL|RTX|PRIO|ALL}.

SCTP_RECONFIG_SUPPORTED
    Enable the Stream Reconfiguration(RECONF) for the future associations. For different type of requests enabling, see SCTP_ENABLE_STREAM_RESET option. The parameter type is struct sctp_assoc_value. For reading, assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC. For writing, assoc_id is SCTP_FUTURE_ASSOC. Default: sysctl_net.sctp.reconf_enable. RFC: RFC6525.

SCTP_ENABLE_STREAM_RESET
    This option allows a user to control whether the kernel processes or denies incoming requests in RECONF chunks. The parameter type is struct sctp_assoc_value. For reading, assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC. For writing, assoc_id is a specified assoc_id or SCTP_{FUTURE|CURRENT|ALL}_ASSOC. assoc_value can be SCTP_ENABLE_{RESET_STREAM_REQ|RESET_ASSOC_REQ|CHANGE_ASSOC_REQ}. Default: 0. Require: SCTP_RECONFIG_SUPPORTED.

SCTP_RESET_STREAMS
    This option allows the user to request the reset of incoming and/or outgoing streams. The parameter type is struct sctp_reset_streams, for writing only. srs_assoc_id is a specified assoc_id. Require: SCTP_ENABLE_STREAM_RESET.

SCTP_RESET_ASSOC
    This option allows a user to request the reset of the SSN/TSN. The parameter type is sctp_assoc_t, for writing only. It is a specified assoc_id. Require: SCTP_ENABLE_STREAM_RESET.

SCTP_ADD_STREAMS
    This option allows a user to request the addition of a number of incoming and/or outgoing streams. The parameter type is struct sctp_add_streams, for writing only. sas_assoc_id is a specified assoc_id. Require: SCTP_ENABLE_STREAM_RESET.

SCTP_STREAM_SCHEDULER
    This option is used to select a stream scheduler for data sending. The parameter type is struct sctp_assoc_value. For reading, assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC. For writing, assoc_id is a specified assoc_id or SCTP_{FUTURE|CURRENT|ALL}_ASSOC. assoc_value can be SCTP_SS_{FCFS|PRIO|RR|FC|WFQ}. Default: SCTP_SS_FCFS. RFC: RFC8260.

SCTP_STREAM_SCHEDULER_VALUE
    Some stream schedulers require additional information to be set for individual streams. The parameter type is struct sctp_assoc_value. For reading, assoc_id is a specified assoc_id. For writing, assoc_id is a specified assoc_id or SCTP_CURRENT_ASSOC. Require: SCTP_STREAM_SCHEDULER.

SCTP_INTERLEAVING_SUPPORTED
    This socket option allows the enabling or disabling of the negotiation of user message interleaving support for future associations. The parameter type is struct sctp_assoc_value. For reading, assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC. For writing, assoc_id is SCTP_FUTURE_ASSOC. Default: sysctl_net.sctp.intl_enable. Require: SCTP_FRAGMENT_INTERLEAVE. RFC: RFC8260.

SCTP_ASCONF_SUPPORTED
    Enable the Dynamic Address Reconfiguration(ASCONF) for the future associations. The parameter type is struct sctp_assoc_value. For reading, assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC. For writing, assoc_id is SCTP_FUTURE_ASSOC. Default: sysctl_net.sctp.addip_enable. RFC: RFC5061.

SCTP_AUTO_ASCONF
    This option will enable or disable the use of the automatic generation of ASCONF chunks to add and delete addresses to an existing association. Note that this option has two caveats, namely a) it only affects sockets that are bound to all addresses available to the SCTP stack, and b) the system administrator may have an overriding control that turns the ASCONF feature off no matter what setting the socket option may have. The parameter type is int boolean, for reading and writing. Default: sysctl_net.sctp.default_auto_asconf.

SCTP_AUTH_SUPPORTED
    Enable AUTH for the future associations. The parameter type is struct sctp_assoc_value. For reading, assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC. For writing, ssoc_id is SCTP_FUTURE_ASSOC. Default: sysctl_net.sctp.auth_enable. RFC: RFC4895.

SCTP_ECN_SUPPORTED
    Enable ECN for the future associations. The parameter type is struct sctp_assoc_value. For reading, assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC. For writing, assoc_id is SCTP_FUTURE_ASSOC. Default: sysctl_net.sctp.ecn_enable.

SCTP_REMOTE_UDP_ENCAPS_PORT
    This option is used to set the encapsulation port(a remote listening or dest port) for SCTP over UDP, which allows SCTP traffic to pass through legacy NATs that do not provide native SCTP support. The parameter type is struct sctp_udpencaps, for reading and writing. sue_address is a specified transport address or 0, sue_assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC. Default: sysctl_net.sctp.encap_port. RFC: RFC6951.

SCTP_PLPMTUD_PROBE_INTERVAL
    This option is used to configure the PROBE_INTERVAL for the Packetization Layer Path MTU Discovery(PLPMTUD). It can be set to a value >= 5000 or 0(disabled). The parameter type is struct sctp_probeinterval, for reading and writing. spi_address is a specified transport address or 0, spi_assoc_id is a specified assoc_id or SCTP_FUTURE_ASSOC. Default: 0(disabled). RFC: RFC8899.

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.