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Capture network traffic on a port with tcpdump

harmless rootNetworkalle
Adjust the values, the command updates live
root@server
tcpdump -i any -nn -c 100 port 25

Shows the packets on all interfaces that involve the given port and exits after the given count. -nn disables DNS and port name resolution and keeps the output fast. This clarifies whether requests reach the server at all and whether it replies.

Note: With -w datei.pcap the capture is saved for Wireshark. If needed, install the package with apt install tcpdump.

Also searched as

  • tcpdump capture specific port
  • check if traffic reaches server
  • sniff packets on port 25

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