Patches to improve SYN performance when under attack
Jonathan T. Looney
jtl at freebsd.org
Mon May 9 16:16:21 UTC 2016
On 5/7/16, 11:17 AM, "owner-freebsd-transport at freebsd.org on behalf of George Neville-Neil" <owner-freebsd-transport at freebsd.org on behalf of gnn at neville-neil.com> wrote:
>Can folks take a quick look at these?
My quick 2c (since all you asked for was "quick" :-) ):
With SYN cookies, I don't think either of these matter.
With the syncache, both might.
In 11.1, I believe cookies are the default.
>> From: Robert N. M. Watson <robert.watson at cl.cam.ac.uk>
>> To: George V. Neville-Neil <gnn at neville-neil.com>
>> Subject: Fwd: Patches to improve SYN performance when under attack
>> Date: Wed, 27 Apr 2016 15:31:34 +0100
>> Possibly something for the TCP group to talk about sometime.
>>> Begin forwarded message:
>>> From: Richard Clayton <richard at highwayman.com>
>>> Subject: Patches to improve SYN performance when under attack
>>> Date: 27 April 2016 at 15:20:20 BST
>>> To: Robert Watson <robert.watson at cl.cam.ac.uk>
>>> As discussed, first patch is Oct 2015, second Apr 2016
>>> This patch series takes the steps to use normal TCP/DCCP ehash
>>> table to store SYN_RECV requests, instead of the private per-
>>> listener hash table we had until now.
>>> SYNACK skb are now attached to their syn_recv request socket, so
>>> that we no longer heavily modify listener sk_wmem_alloc.
>>> listener lock is no longer held in fast path, including SYNCOOKIE
>>> During my tests, my server was able to process 3,500,000 SYN
>>> packets per second on one listener and still had available cpu
>>> That is about 2 to 3 order of magnitude what we had with older
>>> Last known hot point during SYNFLOOD attack is the clearing of
>>> rx_opt.saw_tstamp in tcp_rcv_state_process()
>>> It is not needed for a listener, so we move it where it matters.
>>> Performance while a SYNFLOOD hits a single listener socket went
>>> from 5 Mpps to 6 Mpps on my test server (24 cores, 8 NIC RX queues)
>>> richard @ highwayman . com "Nothing seems the same
>>> Still you never see the change from day to day
>>> And no-one notices the customs slip away"
>freebsd-transport at freebsd.org mailing list
>To unsubscribe, send any mail to "freebsd-transport-unsubscribe at freebsd.org"
More information about the freebsd-transport