From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCH net-next v14 3/7] sch_cake: Add optional ACK filter
Date: Mon, 21 May 2018 14:15:11 -0700
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Cc: Yuchung Cheng <ycheng@google.com>,
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On 05/21/2018 01:35 PM, Toke Høiland-Jørgensen wrote:

> +
> +	/* 3 reserved flags must be unset to avoid future breakage
> +	 * ECE/CWR/NS can be safely ignored
> +	 * ACK must be set
> +	 * All other flags URG/PSH/RST/SYN/FIN must be unset
> +	 * 0x0FFF0000 = all TCP flags (confirm ACK=1, others zero)
> +	 * 0x01C00000 = NS/CWR/ECE (safe to ignore)
> +	 * 0x0E3F0000 = 0x0FFF0000 & ~0x01C00000
> +	 */
> +	if (((tcp_flag_word(tcph) &
> +	      cpu_to_be32(0x0E3F0000)) != TCP_FLAG_ACK))
> +		return false;
>


Why ECE/CWR/NS can be ignored ?

DCTCP would disagree, and maybe BBR soon.