diff options
| author | Chia-Yu Chang <chia-yu.chang@nokia-bell-labs.com> | 2026-01-31 23:25:09 +0100 |
|---|---|---|
| committer | Paolo Abeni <pabeni@redhat.com> | 2026-02-03 15:13:24 +0100 |
| commit | f326f1f17f3772dae4b37360c639ed6b76fe6354 (patch) | |
| tree | f5630d5f39ee666b78b7e111ab0e6449be1ffaf4 /net/ipv4 | |
| parent | f1eaea5585e4d193e007d671f0916f4371c72c0b (diff) | |
tcp: accecn: retransmit SYN/ACK without AccECN option or non-AccECN SYN/ACK
For Accurate ECN, the first SYN/ACK sent by the TCP server shall set
the ACE flag (Table 1 of RFC9768) and the AccECN option to complete the
capability negotiation. However, if the TCP server needs to retransmit
such a SYN/ACK (for example, because it did not receive an ACK
acknowledging its SYN/ACK, or received a second SYN requesting AccECN
support), the TCP server retransmits the SYN/ACK without the AccECN
option. This is because the SYN/ACK may be lost due to congestion, or a
middlebox may block the AccECN option. Furthermore, if this retransmission
also times out, to expedite connection establishment, the TCP server
should retransmit the SYN/ACK with (AE,CWR,ECE) = (0,0,0) and without the
AccECN option, while maintaining AccECN feedback mode.
This complies with Section 3.2.3.2.2 of the AccECN spec RFC9768.
Signed-off-by: Chia-Yu Chang <chia-yu.chang@nokia-bell-labs.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260131222515.8485-10-chia-yu.chang@nokia-bell-labs.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Diffstat (limited to 'net/ipv4')
| -rw-r--r-- | net/ipv4/tcp_output.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index a1596fe8dd9f..22728daed436 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -1106,7 +1106,7 @@ static unsigned int tcp_synack_options(const struct sock *sk, if (treq->accecn_ok && READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_option) && - req->num_timeout < 1 && remaining >= TCPOLEN_ACCECN_BASE) { + synack_type != TCP_SYNACK_RETRANS && remaining >= TCPOLEN_ACCECN_BASE) { opts->use_synack_ecn_bytes = 1; remaining -= tcp_options_fit_accecn(opts, 0, remaining); } @@ -4012,7 +4012,7 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst, memset(th, 0, sizeof(struct tcphdr)); th->syn = 1; th->ack = 1; - tcp_ecn_make_synack(req, th); + tcp_ecn_make_synack(req, th, synack_type); th->source = htons(ireq->ir_num); th->dest = ireq->ir_rmt_port; skb->mark = ireq->ir_mark; |