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Matthieu Baerts (NGI0) authored
An MPTCP firewall blackhole can be detected if the following SYN retransmission after a fallback to "plain" TCP is accepted. In case of blackhole, a similar technique to the one in place with TFO is now used: MPTCP can be disabled for a certain period of time, 1h by default. This time period will grow exponentially when more blackhole issues get detected right after MPTCP is re-enabled and will reset to the initial value when the blackhole issue goes away. The blackhole period can be modified thanks to a new sysctl knob: blackhole_timeout. Two new MIB counters help understanding what's happening: - 'Blackhole', incremented when a blackhole is detected. - 'MPCapableSYNTXDisabled', incremented when an MPTCP connection directly falls back to TCP during the blackhole period. Because the technique is inspired by the one used by TFO, an important part of the new code is similar to what can find in tcp_fastopen.c, with some adaptations to the MPTCP case. Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/57Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org> Link: https://patch.msgid.link/20240909-net-next-mptcp-fallback-x-mpc-v1-3-da7ebb4cd2a3@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>
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