Tcpdump

tcpdump

Trace network traffic, all packets send are reported to standard output (terminal). Cheatsheet

-w <filename> -C 10

Dump raw data to <filename>, create new file after 10 million (not 10MB) bytes are written

-r <filename> -tttt -X

Read packets from <filename>, give absolute time and all data

-i <interface>

Trace <interface> only

-n port 53 and ip6 and host <address>

Do not lookup host or port-names, select only packets from port 53, IPv6 protocol and specified host(address)

In the output Flags are reported that have following meaning:

S (SYN)
F (FIN)
P (PUSH)
R (RST), 
U (URG), 
W (ECN CWR), 
E (ECN-Echo)
. (ACK)
none if no flags are set...