Re: [PATCH v9 net-next 07/15] tcp: accecn: retransmit downgraded SYN in AccECN negotiation

On Mon, Jan 19, 2026 at 7:59 PM [off-list ref] wrote:

From: Chia-Yu Chang <redacted>

Based on AccECN spec (RFC9768), if the sender of an AccECN SYN
(the TCP Client) times out before receiving the SYN/ACK, it SHOULD
attempt to negotiate the use of AccECN at least one more time by
continuing to set all three TCP ECN flags (AE,CWR,ECE) = (1,1,1) on
the first retransmitted SYN (using the usual retransmission time-outs).

If this first retransmission also fails to be acknowledged, in
deployment scenarios where AccECN path traversal might be problematic,
the TCP Client SHOULD send subsequent retransmissions of the SYN with
the three TCP-ECN flags cleared (AE,CWR,ECE) = (0,0,0).

Signed-off-by: Chia-Yu Chang <redacted>
Acked-by: Paolo Abeni <pabeni@redhat.com>

Please amend the changelog to give the RFC precise relevant chapter
(3.1.4.1 if I am not mistaken)

Reviewed-by: Eric Dumazet <edumazet@google.com>