From: "krv" <krv@kaevee.com>
To: netfilter@lists.netfilter.org
Subject: Re: Synfloods - SNAT slow down
Date: Fri, 23 Apr 2004 19:13:04 +0530 [thread overview]
Message-ID: <007601c42938$e74199c0$2800a8c0@jupiter> (raw)
In-Reply-To: 200404230801.57077.lists@edeca.net
----- Original Message -----
From: "David Cannings" <lists@edeca.net>
To: <netfilter@lists.netfilter.org>
Sent: Friday, April 23, 2004 12:31 PM
Subject: Re: Synfloods - SNAT slow down
> On Friday 23 April 2004 02:23, krv wrote:
> > We have a Linux gateway (2.4.22) which does NAT for all local hosts.
> > Where there is ICMP or SYN floods to be forwarded, the gateway starts
> > slowing down an there will be serious drop in packets being forwarded.
>
> You could try using the limit match in your FORWARD chain, with --limit
> and --limit-burst to limit the number of ICMP or packets with only the
> SYN flag set per second. Your gateway would still have to process the
> packets, at least as far as deciding to drop them, but would not have to
> forward them on so you might see an improvement in performance.
>
> If you do examine this route, be careful you don't quench good ICMP
> packets as there is no retransmission in ICMP and you'll never know if
> certain wanted messages didn't get through. For example, host X is
> sending you an ICMP flood so netfilter starts to drop ICMP packets, but
> host Y tries to send you a host unreachable message.
>
> Also don't forget that even if you decide not to forward the packets they
> are still there "on the wire", thus you will not see any improvement with
> external speeds.
>
> David
>
I have two thousand hosts and two thousand forward rules :(
Even if I completely block a attacking host, the gateway is getting bogged
down.
The gateway would be processing atleast 30Mbps at peak loads.
KRV
next prev parent reply other threads:[~2004-04-23 13:43 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-04-23 1:23 Synfloods - SNAT slow down krv
2004-04-23 7:01 ` David Cannings
2004-04-23 13:43 ` krv [this message]
2004-04-23 14:37 ` Rob Sterenborg
2004-04-23 14:55 ` krv
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