> On 22 Dec, 2020, at 10:06 pm, xnor <[email protected]> wrote: > > The client initiates the IPv4 TCP connection with: > IP Differentiated Services Field: 0x02 (DSCP: CS0, ECN: ECT(0)) > TCP Flags: 0x0c2 (SYN, ECN, CWR) > Seq=0 Win=64240 Len=0 MSS=1460 WS=256 SACK_PERM=1 > > The server responds: > Differentiated Services Field: 0x00 (DSCP: CS0, ECN: Not-ECT) > Flags: 0x012 (SYN, ACK) > Seq=0 Ack=1 Win=64240 Len=0 MSS=1460 SACK_PERM=1 WS=128 > > Shouldn't the server respond with ECT set in the SYN ACK packet > and possibly also have ECN-related flags set in the TCP header?
Not all servers have ECN support enabled. A SYN-ACK without the ECE bit set indicates it does not. The connection then proceeds as Not-ECT. I'm reasonably sure Akamai has specifically enabled ECN support. A lot of smaller webservers are probably running with the default passive-mode ECN support as well (ie. will negotiate inbound but not initiate outbound). - Jonathan Morton _______________________________________________ Cake mailing list [email protected] https://lists.bufferbloat.net/listinfo/cake
