adding tcpdump useful commands

useful_commands_and_scripts/tcpdump.md

@@ -0,0 +1,22 @@
+# Useful `tcpdump` commands
+
+### TCPDUMP Cheat Sheet
+* [TCPDUMP Cheat Sheet](http://packetlife.net/media/library/12/tcpdump.pdf) is a good resource (I also have a local copy in this repository)
+
+### TCP traffic on port 80-88
+`tcpdump -nvvX -sO -i ethO tcp portrange 80-88`
+
+### Capturing traffic to specific IP address excluding specific subnet
+`tcpdump -I ethO -tttt dst ip and not net 10.10.10.0/24`
+
+### Capturing traffic for a specific subnet
+`tcpdump net 10.1.1`
+
+### Capturing traffic for a given duration in seconds
+`dumpcap -I ethO -a duration: sec -w file myfile.pcap`
+
+### Replaying a PCAP
+`file2cable -i ethO -f file.pcap`
+
+### Replaying packets (to fuzz/DoS)
+`tcpreplay--topspeed --loop=O --intf=ethO pcap_file_to_replay mbps=10|100|1000