From: Eric Dumazet <eric.dumazet@gmail.com>
To: Florian Westphal <fw@strlen.de>
Cc: David Miller <davem@davemloft.net>,
hannes@stressinduktion.org, netdev@vger.kernel.org
Subject: Re: updates to syncookies - timestamps not needed any more (freebsd)
Date: Fri, 12 Jul 2013 07:04:45 -0700 [thread overview]
Message-ID: <1373637885.10804.7.camel@edumazet-glaptop> (raw)
In-Reply-To: <20130712084145.GJ27468@breakpoint.cc>
On Fri, 2013-07-12 at 10:41 +0200, Florian Westphal wrote:
> The main difference to what linux does is to avoid encoding the 'count'
> value (Linux doesn't reseed secret[], and relies on count to detect old
> cookies).
>
> Not having the counter frees up space to encode tcp options in the cookie
> instead of the timestamp.
But still wscale and sack options are disabled.
lpq83:~# echo 0 >/proc/sys/net/ipv4/tcp_timestamps
lpq83:~# tcpdump -p -n -s 0 -i eth4
07:03:37.337563 IP 7.7.7.84.64131 > 7.7.7.83.22: S 1523884225:1523884225(0) win 29200 <mss 1460,sackOK,timestamp 74412758 0,nop,wscale 6>
07:03:37.337588 IP 7.7.7.83.22 > 7.7.7.84.64131: S 572330188:572330188(0) ack 1523884226 win 29200 <mss 1460>
07:03:37.337647 IP 7.7.7.84.64131 > 7.7.7.83.22: . ack 1 win 29200
BTW, following patch allows to test more easily syncookies behavior.
If sysctl_tcp_syncookies is set to 2, we always use syncookies.
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 35675e4..590659e 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1462,7 +1462,8 @@ int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
* limitations, they conserve resources and peer is
* evidently real one.
*/
- if (inet_csk_reqsk_queue_is_full(sk) && !isn) {
+ if ((sysctl_tcp_syncookies == 2 ||
+ inet_csk_reqsk_queue_is_full(sk)) && !isn) {
want_cookie = tcp_syn_flood_action(sk, skb, "TCP");
if (!want_cookie)
goto drop;
next prev parent reply other threads:[~2013-07-12 14:04 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-07-08 16:04 updates to syncookies - timestamps not needed any more (freebsd) Hannes Frederic Sowa
2013-07-08 16:39 ` Eric Dumazet
2013-07-08 18:09 ` Hannes Frederic Sowa
2013-07-11 23:57 ` David Miller
2013-07-12 1:41 ` Hannes Frederic Sowa
2013-07-12 2:25 ` Eric Dumazet
2013-07-12 6:59 ` richard -rw- weinberger
2013-07-12 15:22 ` Rick Jones
2013-07-12 16:18 ` Eric Dumazet
2013-07-12 16:33 ` Rick Jones
2013-07-12 17:00 ` Eric Dumazet
2013-07-12 7:24 ` David Miller
2013-07-12 8:41 ` Florian Westphal
2013-07-12 14:04 ` Eric Dumazet [this message]
2013-07-12 14:25 ` Florian Westphal
2013-07-12 14:32 ` Eric Dumazet
2013-07-12 23:37 ` David Miller
2013-07-26 6:45 ` Hannes Frederic Sowa
2013-07-26 12:56 ` Eric Dumazet
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