Linux – How to Monitor Aborted Connections on Port 80 With tcpdump

apache-2.2linuxtcpdumpunix

Can I use tcpdump to detect Aborted connections on port 80 (Apache) originating from a specific IP (my remote IP). I can reproduce the Aborted connection in my web browser, but I have no way to verify if the request is getting to my server. I tried this, but couldn't really tell if a connection was Aborted.

tcpdump -n -i eth0 -s 0 src or dst port 80|grep -F "XXX.XXX.XXX.XXX"

Best Answer

I would think that an "Aborted" connection happens when a TCP packet is sent the tells the connection to reset, the flag that represents this is the RST flag.

You can filter for RST using tcpdump -i eth1 'tcp[13] & 4 = 4'. Also, a bit off point but grepping tcp dump is a little lazy, you can always add dst host X or src host X to your filter.

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