sctpctrl Command

Purpose

Controls and configures SCTP.

Syntax

sctpctrl {load|dump|set}

sctpctrl stats [reset] [interval]

sctpctrl set {name=value|default [name]}

sctpctrl get [name]

Description

The sctpctrl command is used to control and configure the SCTP kernel extension. This command can be used to load and unload the SCTP kernel extension. This can also be used to dump SCTP data and set or retrieve various SCTP tunable. Further, sctpctrl command can be used to read and reset the SCTP specific network statistics.

Parameters

Tunable Parameters

The sctpctrl command is also used to configure the SCTP tuning parameters. The changes made are not permanent and they have to be set every time a system gets rebooted. The tunables parameters are explained in the following table.

Item	Description
Parameter	Purpose	Scope	Default
sctp_low_rto	When nonzero, this value is used in place of RTO.min (retransmission time-out). It is specified in terms of milliseconds. Values less than 200 are not allowed. The available time-out values are 200, 250, 300, 350, and so on.	This value is examined each time a new RTT (round trip time) measurement is made and also when RTO is adjusted due to packet loss.	As specified in the RFC 4960 (Request for Comment) document, the default value for this tunable is zero, which means the minimum value of RTO.Min is used, which is 1 second.
sctp_enable_shutdown_guard	When nonzero, this tunable enables a T5-shutdown guard-timer. It is not RFC compliant because it begins timing when association enters shutdown-pending state.	This value is only examined at an association shutdown.	The default value for this tunable is zero, which means that the T5-shutdown guard-timer is not used.
sctp_max_init_attempts	This tunable parameter specifies the maximum number of retransmission attempts that are allowed for the retransmission of the INIT packets.		The default value for this tunable parameter is 8.
sctp_max_init_timeo	When the value of this tunable parameter is nonzero, the tunable value is used instead of the RTO.max parameter (retransmission timeout) for INIT packets. It is specified in milliseconds. Values less than 200 milliseconds are not allowed. The available timeout values are 200, 250, 300, 350, and so on.	This tunable parameter specifies the maximum value to be used when the INIT packets are retransmitted.	The default value for this tunable parameter is zero seconds. In this case, the sctp_rttmax tunable parameter is used.
sctp_shutdown_guard_timer	When the sctp_enable_shutdown_guard parameter is a nonzero value, this tunable defines the shutdown time-out value in seconds.	This value is only examined at an association shutdown.	The default value is 300 seconds, which is the RFC-specified value for the T5-shutdown guard-timer.
sctp_peerchangespath	When nonzero, this tunable causes a primary path change based on an incoming data chunk from a different path than the current primary path.	This value is examined on every inbound data chunk.	The default value for this tunable is 1, which retains the existing behavior.
sctp_delack_timer	This tunable specifies the timer value in ticks (1 tick = 50 ms (milliseconds)) for the delayed-ack timer.	For an ACCEPTCONN socket, this value is established during setup and is used for all associations that share that socket. For a socket other than an ACCEPTCONN socket, it is set at association creation. So changes to this tunable do not affect associations already in existence.	The default value is 4 ticks (200 ms).
sctp_drop_gapacks	If set to 1, it causes the sender side to drop all GAPACKED packets from the socket send buffer, thus making some space free for new packets. Note: This is an RFC noncompatible tunable and could impact interoperability with other implementations, potentially resulting in a message loss.	This tunable is checked each time GAPACKED packets are processed.	The default value is 0, which means disabled.
sctp_dontdelayack	If set to 1, a SACK packet is sent for every other DATA packet. Otherwise, a delayed-ack timer is started.	Any updates to this tunable have an immediate impact.	The default value is 1.
sctp_nagle	If set to 1, it ensures that at least 1 MTU (maximum transmission unit) of data is sent.	Any updates to this tunable have an immediate impact.	The default value is 1 (a nagle is enabled).
sctp_maxburst	If nonzero, it limits the maximum number of packets sent out to this value.	Any updates to this tunable have an immediate impact.	The default value is 8 packets.
sctp_rttmax	This tunable specifies the maximum value to be used when RTO computations are made.	Similar to the sctp_low_rto parameter, this value is examined each time a new RTT measurement is made (and RTO calculated with that) and also when RTO is adjusted due to packet loss.	The default value is 60 seconds.
sctp_rttmin	This tunable specifies the minimum value to be used when RTO computations are made.	If the sctp_low_rto parameter is nonzero, this value is ignored. Otherwise, it is examined each time a new RTT measurement is made and when RTO is stopped due to packet loss.	The default value is 1 second, which ensures that the minimum RTO cannot go below that.
sctp_assoc_maxerr	This tunable sets the overall association error count. If an error count exceeds this value, the association is ended. Currently, this value is ignored. The assoc_maxerr parameter is calculated based on the path error count and number of faddrs.	For an ACCEPTCONN socket, this value is established during setup and is used for all associations that share that socket. For a socket that is not an ACCEPTCONN socket, it is set at association creation. So changes to this tunable do not affect associations already in existence.	The default value is 10.
sctp_path_maxerr	This tunable sets the maximum error count for each destination. If the error count exceeds this value, the path is marked down and an alternative path is chosen.	For an ACCEPTCONN socket, this value is established during setup and is used for all associations that share that socket. For a socket that is not an ACCEPTCONN socket, it is set at association creation. So changes to this tunable do not affect associations already in existence.	The default value is 5.
sctp_use_checksum	This tunable allows an administrator to use different checksum computation methods. Possible values follows: 0: CRC32 checksum 1: No checksum computation is made 2: Internet checksum. The packets are dropped if different values are used by two peers.	This parameter is examined for each outgoing and incoming packet.	The default value is zero, which is the RFC-specified CRC32 checksum.
sctp_sendspace	This tunable specifies the socket buffer size for sending data. The optimum buffer size is the product of the media bandwidth and the average round-trip time of a packet: optimum_window = bandwidth * average_round_trip_time	This parameter is accessed when a new association is created. Use the setsockopt function to override this parameter.	The default value is 65536.
sctp_recvspace	This tunable specifies the socket buffer size for receiving data.	This parameter is accessed when a new association is created. Use the setsockopt function to override this parameter.	The default value is 65536.
sctp_send_fewsacks	When enabled, this tunable parameter implements recv side silly window avoidance. It prevents sending a window update until a receiver can fit in 1 MTU of data.	This parameter is accessed each time data is read by an application and a window update is being sent.	The default value is 0.
sctp_cookie_life	This tunable specifies the time duration in seconds for which a cookie is considered to be valid.	This parameter is used to determine a stale cookie during connection establishment.	The default value is 60 seconds.
sctp_ecn	This tunable enables or disables the explicit congestion notification (RFC 3168).	It is accessed during connection establishment.	The default value is 1.
sctp_ephemeral_high	This tunable specifies the largest port number to allocate for the SCTP (Stream Control Transmission Protocol) ephemeral ports.	It is used when an application is trying to bind to a port.	The default value is 65535.
sctp_ephemeral_low	This tunable specifies the lowest port number to allocate for the SCTP ephemeral ports.	It is used when an application is trying to bind to a port.	The default value is 32768.
sctp_instreams	This tunable specifies the default number of inbound streams that an association uses.	It is used during connection establishment.	The default is 2048.
sctp_outstreams	This tunable specifies the default number of outbound streams that an association uses.	It is used during connection establishment.	The default value is 10.
sctp_pmtu_discover	If enabled, sets the Don't Fragment bit in an IP header of an outgoing packet.	It is accessed when the sending packets are sent out.	The default value is 1.
sctp_recv_multibuf	This tunable controls the socket receive buffer accounting. The default value is 0 and it indicates that all the associations belonging to the socket share the same receive buffer space. When set to nonzero, each association has its own receive buffer space of this value. The setsockopt function overrides this value.	It is accessed when an association is being created.	The default value is 0 (multibuf is not used).
sctp_send_multibuf	This tunable controls the socket send buffer accounting. The default value is 0 and indicates that all the associations belonging to a socket share the same send buffer space. When set to nonzero, each association has its own send buffer space of this value. The setsockopt function overrides this value.	It is accessed when an association is being created.	The default is 0 (multibuf is not used).
sctp_failover_type	When enabled, it causes a new path to be chosen after every retransmit timeout. Otherwise, failover happens only after the path error count value exceeds max path error count value.	It is accessed whenever RTO starts (when there is a packet drop).	The default value is 1.
sctp_check_associd	Governs the pattern related to checking the association ID passed by an application when sending an ABORT packet. If set to 0, it ignores the association ID. The association is found by using the foreign address. If set to 1, it performs strict association ID matching. If an association is not found with the passed assoc_id value, an EINVAL error is returned. If set to 2, it performs association ID matching, but uses the foreign address when a reserved assoc_id value is used.	It is accessed whenever a user application issues an ABORT packet.	The default value is 0.

Examples

1. To load the SCTP kernel extension, type the following:

   sctpctrl load

2. To reset the SCTP statistics, type the following:

   sctpctrl stats reset

   This command will zero-out all the SCTP statistics.
3. To get the values of the SCTP tunable, type the following:

   sctpctrl get

   This will list all the SCTP tunable and their values. Here is a sample output.

   sctp_assoc_maxerr = 10
   sctp_cookie_life = 60
   sctp_delack_timer = 4
   sctp_dontdelayack = 1
   sctp_ecn = 1
   sctp_ephemeral_high = 65535
   sctp_ephemeral_low = 32768
   sctp_instreams = 2048
   sctp_maxburst = 8
   sctp_outstreams = 10
   sctp_path_maxerr = 5
   sctp_pmtu_discover = 1
   sctp_rttmax = 60
   sctp_rttmin = 1
   sctp_recvspace = 65536
   sctp_sendspace = 65536
   sctp_send_fewsacks = 0

4. To set sctp_path_maxerr to a value of 6, type the following:

   sctpctrl set sctp_path_maxerr=6 

Location

/usr/sbin/sctpctrl

Files