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Message-ID: <1414770460.27538.9.camel@edumazet-glaptop2.roam.corp.google.com> Date: Fri, 31 Oct 2014 08:47:40 -0700 From: Eric Dumazet <eric.dumazet@...il.com> To: Florian Westphal <fw@...len.de> Cc: netdev@...r.kernel.org Subject: Re: [PATCH -next v2 1/2] syncookies: remove ecn_ok validation when decoding option timestamp On Fri, 2014-10-31 at 15:15 +0100, Florian Westphal wrote: > So if you have a per route ecn setting, and syncookies are used, > and tcp_ecn sysctl is 0: This part I do not understand. Why should tcp_ecn be 0 here, and not 2 (default value) ? > > 1. we receive syn with ecn on and timestamps > 2. we send cookie synack, with timestamp and ecn (route allowed it), > the lower bits of the timestamp have a "magic" bit set that allows > us to infer that ecn was negotiated successfully. > 3. we drop the ack from the client, since timestamp decoding sees > "ecn is on according to timestamp, but the tcp_ecn sysctl is off". > > So to fix this, step 3 either has to check the dst setting > in addition to the global sysctl, or to rely on the timestamp alone > that ecn was requested by the original client and allowed by our host > at the time synack timestamp was generated/sent. > > I hope that explains the reason behind patch #1 up. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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