From: Jonathan Morton <chromatix99@gmail.com>
To: xnor <xnoreq@gmail.com>
Cc: cake@lists.bufferbloat.net
Subject: Re: [Cake] ECN not working?
Date: Tue, 22 Dec 2020 22:15:19 +0200 [thread overview]
Message-ID: <DDC33147-4B1D-45A0-B73B-0641A4050A68@gmail.com> (raw)
In-Reply-To: <421ffd89-0c2c-1187-380c-03a0968f4095@gmail.com>
> On 22 Dec, 2020, at 10:06 pm, xnor <xnoreq@gmail.com> 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
next prev parent reply other threads:[~2020-12-22 20:15 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-22 20:06 xnor
2020-12-22 20:15 ` Jonathan Morton [this message]
2020-12-22 21:44 ` xnor
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