netdev - Re: [PATCH net-next] tcp: avoid tx starvation by SYNACK packets

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Date:	Fri, 1 Jun 2012 18:28:17 -0700
From:	Dave Taht <dave.taht@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Hans Schillstrom <hans.schillstrom@...csson.com>,
	netdev <netdev@...r.kernel.org>,
	Neal Cardwell <ncardwell@...gle.com>,
	Tom Herbert <therbert@...gle.com>,
	Jesper Dangaard Brouer <brouer@...hat.com>
Subject: Re: [PATCH net-next] tcp: avoid tx starvation by SYNACK packets

On Thu, May 31, 2012 at 2:56 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> From: Eric Dumazet <edumazet@...gle.com>
>
> pfifo_fast being the default Qdisc, its pretty easy to fill it with
> SYNACK (small) packets while host is under SYNFLOOD attack.
>
> Packets of established TCP sessions are dropped and host appears almost
> dead.
>
> Avoid this problem assigning TC_PRIO_FILLER priority to SYNACK
> generated in SYNCOOKIE mode, so that these packets are enqueued into
> pfifo_fast band 2.
>
> Other packets, queued to band 0 or 1 are dequeued before any SYNACK
> packets waiting in band 2.

I am curious as to how well fq_codel survives an attack like this, without aid.
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