How to stop the flood?

Rikunj rikunj at
Thu Apr 28 16:47:42 CEST 2005

Thankyou for the reply.

This was the log from one of my client who was attacked from a client on
other subnet.

My network consist of clients from different subnets of /24.

The attacks from one subnet travels through my linux router and hits the
client on other subnet.

I tried few rules as below but seems not to be working.

-----------Cut From

echo 1 > /proc/sys/net/ipv4/tcp_syncookies
echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
echo 0 > /proc/sys/net/ipv4/conf/all/log_martians
echo 0 > /proc/sys/net/ipv4/tcp_timestamps
echo 0 > /proc/sys/net/ipv4/conf/all/accept_redirects
echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
echo 0 > /proc/sys/net/ipv4/conf/all/accept_source_route
echo 1 > /proc/sys/net/ipv4/icmp_ignore_bogus_error_responses
iptables -F
iptables -t nat -F
iptables -t mangle -F
iptables -P FORWARD DROP
iptables -P INPUT DROP
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A FORWARD -p icmp --icmp-type echo-request -m length --length
92 -j DROP
iptables -A INPUT -i lo -j ACCEPT
iptables -A FORWARD -p tcp --syn -m limit --limit 10/s -j ACCEPT
iptables -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A FORWARD -p ip -f  -j DROP
iptables -A FORWARD -p tcp --tcp-flags ALL ACK,RST,SYN,FIN -j DROP
iptables -A FORWARD -p tcp --tcp-flags SYN,FIN SYN,FIN -j DROP
iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN,RST -j DROP
iptables -A INPUT -p tcp --tcp-flags ALL NONE -j DROP
iptables -A INPUT -p tcp --tcp-flags FIN,RST FIN,RST -j DROP
iptables -A INPUT -p tcp --tcp-flags ACK,FIN FIN -j DROP
iptables -A INPUT -p tcp --tcp-flags ACK,PSH PSH -j DROP
iptables -A INPUT -p tcp --tcp-flags ACK,URG URG -j DROP

Rikunj Patel

----- Original Message -----
From: "Jason Opperisano" <opie at>
To: <netfilter at>
Sent: Thursday, April 28, 2005 5:16 PM
Subject: Re: How to stop the flood?

> On Thu, Apr 28, 2005 at 04:35:14PM +0300, Rikunj wrote:
> >
> > Hello All,
> >
> > I am seeing lots of this kind of scanning flood attack from different IP
> > within my
> >
> > network and even from outside.
> >
> > How can I stop and protect from this kind of attack?
> the word "blocked" means, well...blocked.  so you already are
> "protecting"...
> as for "stopping," go to the person sitting at and kick
> their teeth down their throat.
> -j
> --
> "Peter: Wow, it's like I died and went to heaven, then God realized it
>  wasn't my time yet, so He sent me back to a brewery."
>         --Family Guy

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