How to stop the flood?

Jason Opperisano opie at
Thu Apr 28 18:35:34 CEST 2005

On Thu, Apr 28, 2005 at 05:47:42PM +0300, Rikunj wrote:
> 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 OUTPUT ACCEPT
> 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
> -----------------------------------------------

well, you're really not blocking much of anything with that.  if you
wish to block

  iptables -A FORWARD -s -j DROP

when they call to ask why "the Internet is down" invoke plan B--opening
up a can of the genuine whoop-ass.


"Peter: You wanna talk about awkward moments? Once, during sex,
 I called Lois "Frank". Your move, Sherlock."
        --Family Guy

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