On 10/13/25 7:03 PM, chia-yu.chang@nokia-bell-labs.com wrote:
From: Chia-Yu Chang chia-yu.chang@nokia-bell-labs.com
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 chia-yu.chang@nokia-bell-labs.com
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