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tcp: accecn: detect loss ACK w/ AccECN option and add TCP_ACCECN_OPTION_PERSIST

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Detect spurious retransmission of a previously sent ACK carrying the
AccECN option after the second retransmission. Since this might be caused
by the middlebox dropping ACK with options it does not recognize, disable
the sending of the AccECN option in all subsequent ACKs. This patch
follows Section 3.2.3.2.2 of AccECN spec (RFC9768), and a new field
(accecn_opt_sent_w_dsack) is added to indicate that an AccECN option was
sent with duplicate SACK info.

Also, a new AccECN option sending mode is added to tcp_ecn_option sysctl:
(TCP_ECN_OPTION_PERSIST), which ignores the AccECN fallback policy and
persistently sends AccECN option once it fits into TCP option space.

Signed-off-by: Chia-Yu Chang <chia-yu.chang@nokia-bell-labs.com>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260131222515.8485-13-chia-yu.chang@nokia-bell-labs.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Chia-Yu Chang
2026-01-31 23:25:12 +01:00
committed by Paolo Abeni
parent 2ed661248e
commit 1247fb19ca
6 changed files with 26 additions and 5 deletions
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4
Documentation/networking/ip-sysctl.rst
View File

@@ -482,7 +482,9 @@ tcp_ecn_option - INTEGER
1 Send AccECN option sparingly according to the minimum option
rules outlined in draft-ietf-tcpm-accurate-ecn.
2 Send AccECN option on every packet whenever it fits into TCP
option space.
option space except when AccECN fallback is triggered.
3 Send AccECN option on every packet whenever it fits into TCP
option space even when AccECN fallback is triggered.
= ============================================================
Default: 2