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5b4fd35343
The number of SYN + MPC retransmissions before falling back to TCP was
fixed to 2. This is certainly a good default value, but having a fixed
number can be a problem in some environments.
The current behaviour means that if all packets are dropped, there will
be:
- The initial SYN + MPC
- 2 retransmissions with MPC
- The next ones will be without MPTCP.
So typically ~3 seconds before falling back to TCP. In some networks
where some temporally blackholes are unfortunately frequent, or when a
client tries to initiate connections while the network is not ready yet,
this can cause new connections not to have MPTCP connections.
In such environments, it is now possible to increase the number of SYN
retransmissions with MPTCP options to make sure MPTCP is used.
Interesting values are:
- 0: the first retransmission will be done without MPTCP options: quite
aggressive, but also a higher risk of detecting false-positive
MPTCP blackholes.
- >= 128: all SYN retransmissions will keep the MPTCP options: back to
the < 6.12 behaviour.
The default behaviour is not changed here.
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20250117-net-next-mptcp-syn_retrans_before_tcp_fallback-v1-1-ab4b187099b0@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.