SCTP Tunable Parameters

`sctp_max_init_retr`

Description: Controls the maximum number of attempts an SCTP endpoint should make at resending an INIT chunk. The SCTP endpoint can use the SCTP initiation structure to override this value.
Default: 8

Range: 0 to 128
Dynamic?: Yes
When to Change: The number of INIT retransmissions depend on sctp_pa_max_retr. Ideally, sctp_max_init_retr should be less than or equal to sctp_pa_max_retr.
Commitment Level: Unstable

`sctp_pa_max_retr`

Description: Controls the maximum number of retransmissions (over all paths) for an SCTP association. The SCTP association is aborted when this number is exceeded.
Default: 10

Range: 1 to 128
Dynamic?: Yes
When to Change: The maximum number of retransmissions over all paths depend on the number of paths and the maximum number of retransmission over each path. Ideally, sctp_pa_max_retr should be set to the sum of sctp_pp_max_retr over all available paths. For example, if there are 3 paths to the destination and the maximum number of retransmissions over each of the 3 paths is 5, then sctp_pa_max_retr should be set to less than or equal to 15. (See the Note in Section 8.2, RFC 2960.)
Commitment Level: Unstable

`sctp_pp_max_retr`

Description: Controls the maximum number of retransmissions over a specific path. When this number is exceeded for a path, the path (destination) is considered unreachable.
Default: 5

Range: 1 to 128
Dynamic?: Yes
When to Change: Do not change this value to less than 5.
Commitment Level: Unstable

`sctp_cwnd_max`

Description: Controls the maximum value of the congestion window for an SCTP association.
Default: 1,048,576
Range: 128 to 1,073,741,824
Dynamic?: Yes
When to Change: Even if an application uses setsockopt(3XNET) to change the window size to a value higher than sctp_cwnd_max, the actual window used can never grow beyond sctp_cwnd_max. Thus, sctp_max_buf should be greater than sctp_cwnd_max.
Commitment Level: Unstable

`sctp_ipv4_ttl`

Description: Controls the time to live (TTL) value in the IP version 4 header for the outbound IP version 4 packets on an SCTP association.
Default: 64

Range: 1 to 255
Dynamic?: Yes
When to Change: Generally, you do not need to change this value. Consider increasing this parameter if the path to the destination is likely to span more than 64 hops.
Commitment Level: Unstable

`sctp_heartbeat_interval`

Description

Computes the interval between HEARTBEAT chunks to an idle destination, that is allowed to heartbeat.

An SCTP endpoint periodically sends an HEARTBEAT chunk to monitor the reachability of the idle destinations transport addresses of its peer.

Default

30 seconds

Range

0 to 86,400 seconds

Dynamic?

Yes

When to Change

Refer to RFC 2960, section 8.3.

Commitment Level

Unstable

`sctp_new_secret_interval`

Description: Determines when a new secret needs to be generated. The generated secret is used to compute the MAC for a cookie.
Default: 2 minutes

Range: 0 to 1,440 minutes
Dynamic?: Yes
When to Change: Refer to RFC 2960, section 5.1.3.
Commitment Level: Unstable

`sctp_initial_mtu`

Description: Determines the initial maximum send size for an SCTP packet including the length of the IP header.
Default: 1500 bytes

Range: 68 to 65,535
Dynamic?: Yes
When to Change: Increase this parameter if the underlying link supports frame sizes that are greater than 1500 bytes.
Commitment Level: Unstable

`sctp_deferred_ack_interval`

Description: Sets the time-out value for SCTP delayed acknowledgment (ACK) timer in milliseconds.
Default: 100 milliseconds

Range: 1 to 60,000 milliseconds
Dynamic?: Yes
When to Change: Refer to RFC 2960, section 6.2.
Commitment Level: Unstable

`sctp_ignore_path_mtu`

Description: Enables or disables path MTU discovery.
Default: 0 (disabled)

Range: 0 (disabled) or 1 (enabled)
Dynamic?: Yes
When to Change: Enable this parameter if you want to ignore MTU changes along the path. However, doing so might result in IP fragmentation if the path MTU decreases.
Commitment Level: Unstable

`sctp_initial_ssthresh`

Description: Sets the initial slow start threshold for a destination address of the peer.
Default: 102,400

Range: 1024 to 4,294,967,295
Dynamic?: Yes
When to Change: Refer to RFC 2960, section 7.2.1.
Commitment Level: Unstable

`sctp_xmit_hiwat`

Description: Sets the default send window size in bytes. See also sctp_max_buf.
Default: 102,400

Range: 8,192 to 1,073,741,824
Dynamic?: Yes
When to Change: An application can use getsockopt(3SOCKET) SO_SNDBUF to change the individual association's send buffer.
Commitment Level: Unstable

`sctp_xmit_lowat`

Description: Controls the lower limit on the send window size.
Default: 8,192

Range: 8,192 to 1,073,741,824
Dynamic?: Yes
When to Change: Generally, you do not need to change this value. This parameter sets the minimum size required in the send buffer for the socket to be marked writable. If required, consider changing this parameter in accordance with sctp_xmit_hiwat.
Commitment Level: Unstable

`sctp_recv_hiwat`

Description: Controls the default receive window size in bytes. See also sctp_max_buf.
Default: 102,400

Range: 8,192 to 1,073,741,824
Dynamic?: Yes
When to Change: An application can use getsockopt(3SOCKET) SO_RCVBUF to change the individual association's receive buffer.
Commitment Level: Unstable

`sctp_max_buf`

Description: Controls the maximum buffer size in bytes. It controls how large the send and receive buffers are set to by an application that uses getsockopt(3SOCKET).
Default: 1,048,576

Range: 8,192 to 1,073,741,824
Dynamic?: Yes
When to Change: Increase the value of this parameter to match the network link speed if associations are being made in a high-speed network environment.
Commitment Level: Unstable

`sctp_ipv6_hoplimit`

Description: Sets the value of the hop limit in the IP version 6 header for the outbound IP version 6 packets on an SCTP association.
Default: 60

Range: 0 to 255
Dynamic?: Yes
When to Change: Generally, you do not need to change this value. Consider increasing this parameter if the path to the destination is likely to span more than 60 hops.
Commitment Level: Unstable

`sctp_rto_min`

Description: Sets the lower bound for the retransmission timeout (RTO) in milliseconds for all the destination addresses of the peer.
Default: 1,000

Range: 500 to 60,000
Dynamic?: Yes
When to Change: Refer to RFC 2960, section 6.3.1.
Commitment Level: Unstable

`sctp_rto_max`

Description: Controls the upper bound for the retransmission timeout (RTO) in milliseconds for all the destination addresses of the peer.
Default: 60,000

Range: 1,000 to 60,000,000
Dynamic?: Yes
When to Change: Refer to RFC 2960, section 6.3.1.
Commitment Level: Unstable

`sctp_rto_initial`

Description: Controls the initial retransmission timeout (RTO) in milliseconds for all the destination addresses of the peer.
Default: 3,000

Range: 1,000 to 60,000,000
Dynamic?: Yes
When to Change: Refer to RFC 2960, section 6.3.1.
Commitment Level: Unstable

`sctp_cookie_life`

Description: Sets the lifespan of a cookie in milliseconds.
Default: 60,000

Range: 10 to 60,000,000
Dynamic?: Yes
When to Change: Generally, you do not need to change this value. This parameter might be changed in accordance with sctp_rto_max.
Commitment Level: Unstable

`sctp_max_in_streams`

Description: Controls the maximum number of inbound streams permitted for an SCTP association.
Default: 32

Range: 1 to 65,535
Dynamic?: Yes
When to Change: Refer to RFC 2960, section 5.1.1.
Commitment Level: Unstable

`sctp_initial_out_streams`

Description: Controls the maximum number of outbound streams permitted for an SCTP association.
Default: 32

Range: 1 to 65,535
Dynamic?: Yes
When to Change: Refer to RFC 2960, section 5.1.1.
Commitment Level: Unstable

`sctp_shutack_wait_bound`

Description: Controls the maximum time, in milliseconds, to wait for a SHUTDOWN ACK after having sent a SHUTDOWN chunk.
Default: 60,000

Range: 0 to 300,000
Dynamic?: Yes
When to Change: Generally, you do not need to change this value. This parameter might be changed in accordance with sctp_rto_max.
Commitment Level: Unstable

`sctp_maxburst`

Description: Sets the limit on the number of segments to be sent in a burst.
Default: 4

Range: 2 to 8
Dynamic?: Yes
When to Change: You do not need to change this parameter. You might change it for testing purposes.
Commitment Level: Unstable

`sctp_addip_enabled`

Description: Enables or disables SCTP dynamic address reconfiguration.
Default: 0 (disabled)

Range: 0 (disabled) or 1 (enabled)
Dynamic?: Yes
When to Change: The parameter can be enabled if dynamic address reconfiguration is needed. Due to security implications, enable this parameter only for testing purposes.
Commitment Level: Unstable

`sctp_prsctp_enabled`

Description: Enables or disables the partial reliability extension (RFC 3758) to SCTP.
Default: 1 (enabled)

Range: 0 (disabled) or 1 (enabled)
Dynamic?: Yes
When to Change: Disable this parameter if partial reliability is not supported in your SCTP environment.
Commitment Level: Unstable