Synner is a custom eth->ip->tcp packet generator (spoofer) for testing firewalls and dos attacks. It is capable of sending large amounts of prebuilt tcp packets (very quickly) with user defined ips, macs, tcp flags, window sizes, payload lengths and more.
You can download it from the following link: https://packetstormsecurity.com/files/download/69802/synner.c
Source: https://packetstormsecurity.com/files/69802/synner.c.html