esnet/iperf 3.21

iperf-3.21

on GitHub

iperf-3.21 2026-04-09

• Notable user-visible changes

  • Support has been added for Global Segmentation Offload (GSO) and
    Global Receive Offload (GRO) under Linux (PR #1925, PR #2007,
    also note that a number of other pull requests were submitted
    towards this functionality).

  • The --bind-dev option is now supported on macOS (PR #1945).

  • Support has been added on macOS for the equivalent of the
    tcp_info structure (#1411, PR #2008). This change results in
    TCP window information being printed in human-readable output
    and a number of TCP statistics being added to the JSON output.

  • The iperf3 server provides more information about various error
    conditions to the client (PR #1914, PR #1931, PR #1950).

  • The maximum value for the --set-mss option is now 32K (PR
    #1816). Note that this option still does not work reliably in
    all cases.

  • The cancellation type of child threads was changed from
    PTHREAD_CANCEL_ASYNCHRONOUS to PTHREAD_CANCEL_DEFERRED
    (#1991, #2003, PR #2004). This change fixes some hangs that
    could occur at the end of a test.

  • A race condition leading to a crash when closing sockets at the
    end of a test has been fixed (PR #1990).

  • iperf3 no longer erroneously prints that zero UDP packets were
    lost during a lossy UDP test (#1984, PR #1988).

  • A division by zero error has been avoided (PR #2002).

  • The security posture of the iperf3.service file has been
    improved considerably by updating a number of settings (PR
    #1855). Note that this file is neither installed nor activated
    by default.

• Notable developer-visible changes

  • iperf3 finally performs ldconfig as a part of make install
    on platforms that require it (#1995, PR #2005).

  • Various bug fixes (PR #1960, PR #1981, PR #2001).

  • Various documentation fixes (PR #1972, PR #1974, PR #1993).