How to capture TCP SYN, ACK and FIN packets with tcpdump

Question: I want to monitor TCP connection dynamics (e.g., three-way handshake for connection establishment, and four-way handshake for connection tear-down). For that, I need to capture only TCP control packets such as those with SYN, ACK or FIN flag set. How can I use tcpdump to capture TCP SYN, ACK, and/or FYN packets only? As […]
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How to fix tcpdump error with file permission denied

Question: When I run tcpdump with “-r” option to read from a packet dump file, I am getting an error from tcpdump saying that “file permission denied”. I am getting this error even when I run tcpdump with root privilege. How can I fix this error? If this problem happens on Ubuntu, it is possible […]
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