On Mon, Jan 19, 2026 at 7:59 PM <[email protected]> wrote: > > From: Chia-Yu Chang <[email protected]> > > For Accurate ECN, the first SYN/ACK sent by the TCP server shall set the > ACE flag (see 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. >
Reviewed-by: Eric Dumazet <[email protected]>
