In case you are searching to explore rule-sets in firewall and finding entry point to a target network or system, the packet crafting technique can be really useful to you. Various great packet crafting utilities exist on the web that will work for you.
Hping
This TCP/IP packet analyzer/assembler is command-line focused. hping’s interface inspirations is analogous to ping(8) command in unix, however, hping is able to send ICMP requests and supports UDP, RAW-IP and TCP protocols with ability to propel files between covered channel and trace route mode among other features.
Scapy
This is a potent and interactive packet exploitation application. It is capable of forging or decoding packets in various protocols, propels them in the cable, capture, match replies and request among others. Scapy is capable of handling many classical tasks such as trace routing, scanning, unit tests, probing, attacks or even network discovery (can substitute hping, 85% of arpspoof, nmap, tethereal, arping, asp-sk, p0f, tcpdump etc.)
Netcat
This easy UNIX utility is capable of reading and writing data in network connections that use UDP or TCP protocol. Net cat is developed to ensure a consistent “backend” tool capable of direct use or driven simply by scripts or programs.
Yersinia
This network tool is developed to capitalize on some weaknesses within diverse network protocols. Yersinia acts as a strong framework for testing and analyzing deployed systems and networks.
Nemesis
This network packet creating as well as injection tool relies on command line in Windows and Unix-like systems. It is suitable in testing firewalls, Network Intrusion Detection Systems and IP stacks among other tasks. Nemesis being command-line driven is ideal for scripting and automation.