sack Parameter

Description

If set to active, TCP always sends a SYN segment with the selective acknowledgment (SACK) permitted option. If TCP receives a SYN segment with a SACK-permitted option and this parameter is set to passive TCP responds with a SACK-permitted option. If the parameter is set to never TCP does not send a SACK-permitted option, regardless of whether the incoming segment contains the SACK permitted option.

Refer to RFC 2018 for information about the SACK option.

Default

active

Range

never, passive, or active

Dynamic?

Yes

When to Change

SACK processing can improve TCP retransmission performance so it should be actively enabled. Sometimes, the other side can be confused with the SACK option actively enabled. If this confusion occurs, set the value to passive so that SACK processing is enabled only when incoming connections allow SACK processing.

Commitment Level

Stable