> -----Original Message----- > From: Paolo Abeni <[email protected]> > Sent: Thursday, October 16, 2025 11:14 AM > To: Chia-Yu Chang (Nokia) <[email protected]>; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; Koen De Schepper (Nokia) > <[email protected]>; [email protected]; > [email protected]; [email protected]; cheshire > <[email protected]>; [email protected]; [email protected]; Vidhi Goel > <[email protected]> > Subject: Re: [PATCH v4 net-next 08/13] tcp: accecn: retransmit SYN/ACK > without AccECN option or non-AccECN SYN/ACK > > > CAUTION: This is an external email. Please be very careful when clicking > links or opening attachments. See the URL nok.it/ext for additional > information. > > > > On 10/13/25 7:03 PM, [email protected] wrote: > > From: Chia-Yu Chang <[email protected]> > > > > If the TCP Server has not received an ACK to acknowledge its SYN/ACK > > after the normal TCP timeout or it receives a second SYN with a > > request for AccECN support, then either the SYN/ACK might just have > > been lost, e.g. due to congestion, or a middlebox might be blocking > > AccECN Options. To expedite connection setup in deployment scenarios > > where AccECN path traversal might be problematic, the TCP Server > > SHOULD retransmit the SYN/ACK, but with no AccECN Option. > > > > If this retransmission times out, to expedite connection setup, the > > TCP Server SHOULD retransmit the SYN/ACK with (AE,CWR,ECE) = (0,0,0) > > and no AccECN Option, but it remains in AccECN feedback mode. > > > > This follows Section 3.2.3.2.2 of AccECN spec (RFC9768). > > > > Signed-off-by: Chia-Yu Chang <[email protected]> > > --- > > include/net/tcp_ecn.h | 14 ++++++++++---- net/ipv4/tcp_output.c | 2 > > +- > > 2 files changed, 11 insertions(+), 5 deletions(-) > > > > diff --git a/include/net/tcp_ecn.h b/include/net/tcp_ecn.h index > > c66f0d944e1c..97a3a7f36aff 100644 > > --- a/include/net/tcp_ecn.h > > +++ b/include/net/tcp_ecn.h > > @@ -651,10 +651,16 @@ static inline void tcp_ecn_clear_syn(struct sock > > *sk, struct sk_buff *skb) static inline void > > tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th) > > { > > - if (tcp_rsk(req)->accecn_ok) > > - tcp_accecn_echo_syn_ect(th, tcp_rsk(req)->syn_ect_rcv); > > - else if (inet_rsk(req)->ecn_ok) > > - th->ece = 1; > > + if (req->num_retrans < 1 || req->num_timeout < 1) { > > I think the above condition does not match the commit message. Should be: > if (!req->num_retrans && !req->num_timeout) { > > /P
Hi Paolo, This patch includes two differetn SYN/ACK retransmissions: In the first retransmited SYN/ACK, the retransmitted SYN/ACK will not include AccECN option. This uses the condition of "req->num_retrans >1" in tcp_synack_options(). In the second retransmitted SYN/ACK, the retransmitted SYN/ACK will further set ACE=0. This uses the condition of "req->num_retrans>1 && req->num_timeout>1" in tcp_ecn_make_synack(). I was thinking, in the next version, I could update the commit message to clarify it. Chia-Yu
