Sometimes when you have a proxy redirection in between, the routing could be asymmetric, which means the reverse packets may flow on a different route based on the routing table and network topology. ![]() One thing to remember is that the handshake, mostly on the TCP layer, can work only when the packets flow in both directions to each other. Usually, if the ping traffic flows then, most others also can. To do this, we must filter based on the IP address or protocol header or port numbers or a combination of this data.Ī basic ping ICMP checks traffic and connectivity after the IPsec VPN setup. One cannot study the contents of a particular packet exchange between two hosts on the Internet without isolating the traffic between a particular set of ports. Once identified, inspect the payloads and extract the data using a file transfer or a file upload using HTTP or even voice, video, or streaming traffic. The start of a connection has SYN packets (Flag of ), while the end will have a reset (Flag of ), OR it could be a FIN from the client, as they close that TCP connection. In using a protocol sniffer, the most important thing is identifying what headers and handshake packets mean. ![]() If you are bored at home in these COVID times, how about extracting the video of a video conference capture? (On a serious note, only do this for your video with the participants' permission.) This article explores how Linux's command-line power, combined with the tcpdump lexical parser's filter expressions, can be used for some complex networking debugging. ![]() ![]() We have all have heard of network analyzers or packet sniffers, Wireshark with its command-line counterpart Tshark, or tcpdump.
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