Re: How to test synflood prevention

[Peggy Kam <ppkam@n-dsi.com>]

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Hi,

I tried to use netcat for generating flood and listening on one machine,
    ie. ./flood.sh attacked_machine_ip attacked_port 1000 | 
/prod/netcat/bin nc -l -p 2222

And tried to do ./nc ip_address_of_the_above_machine 2222 -x -t

I have also set up the firewall as follows:
iptables -N SYN_FLOOD
iptables -i eth1 -A INPUT -p tcp --syn -j SYN_FLOOD
iptables -A SYN_FLOOD -m limit --limit 2/s --limit-burst 4 -j RETURN
iptables -A SYN_FLOOD -j DROP
iptables -A SYN_FLOOD -i eth1 -p tcp ! --syn -m state --state NEW -j DROP

And I have been getting packets transfer between the 2 machines.

May I ask how I can debug the network using this tool netcat.  I am not 
familar with the raw socket stuff at all.  Any help on this is appreciated.

Thanks in advance,
Peggy


Daniel Chemko wrote:

>Try using raw sockets and cook your own headers, or just use tools that
>are designed for it, like netcat
>
>Peggy Kam wrote:
>  
>
>>Hi,
>>
>>I have set up some rules for preventing the synflood attack, ie:
>>
>>iptables -A SYN_FLOOD -m limit --limit 2/s --limit-burst 4 -j ACCEPT
>>iptables -A SYN_FLOOD -j DROP
>>iptables -A SYN_FLOOD -i eth1 -p tcp ! --syn -m state --state NEW -j
>>DROP 
>>
>>However, the firewall does not seem to filter any packets.  I have
>>used 
>>the following tcpflood.c program to generate the flood, however, when
>>I used tcpdump and checked the message log with the firewall with and
>>without the above rules, they gave me the same results.  So, may I ask
>>how I can test the firewall for DoS attack?
>>
>>Thanks in advance,
>>Peggy
>>
>>
>>
>>#tcpflood.c
>>
>>#include <unistd.h>
>>#include <stdio.h>
>>#include <netdb.h>
>>#include <stdlib.h>
>>#include <string.h>
>>#include <unistd.h>
>>#include <sys/socket.h>
>>#include <netinet/in.h>
>>#include <arpa/inet.h>
>>#include <sys/types.h>
>>
>>
>>int main(int argc, char **argv) {
>>
>>  struct sockaddr_in to_addr;
>>  int s;
>>
>>  bzero(&to_addr, sizeof(to_addr));
>>  to_addr.sin_family=AF_INET;
>>
>>
>>  if ( argc == 3 ) {
>>        to_addr.sin_addr.s_addr=inet_addr(argv[1]);
>>        to_addr.sin_port=htons(atoi(argv[2]));
>>  }
>>
>>  else {
>>        fprintf(stderr, "Usage: %s <IP> <PORT>\n", argv[0]);
>>        return 1;
>>  }
>>
>>  printf("Flooding  %s:%d ...\n", argv[1], atoi(argv[2]));
>>
>>  while (1) {
>>
>>        if ((s = socket(PF_INET, SOCK_STREAM, 0)) < 0) {
>>                fprintf(stderr, "Error: socket()\n");
>>                return 1;
>>        }
>>
>>        if ((connect(s, (struct sockaddr *)&to_addr, sizeof to_addr))
>>                < 0) { perror("connect()");
>>                return 1;
>>        }
>>
>>
>>        printf(".");
>>        fflush(stdout);
>>        close(s);
>>
>>  }
>>
>>  return 0;
>>
>>}
>>
>
>  
>

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