In modern times the telnet protocol is no longer in common use and many times systems do not come installed with telnet at all. In the old days, when telnet was popular in use, you could use it to connect to a remote system to validate a port was operational and send raw commands to it. It operates a little like tcpdump except it carries a lot of the logic with it on filtering and extra command line options. Tshark is the CLI companion to Wireshark. It also does a great job at understanding most protocols and providing you the metadata of them in easy to read formats. In other cases you can decode VoIP streams to listen to the audio and verify the quality. It is also very extensible and has many extensions to aid in visualization that go above and beyond what tcpdump provides.įor example, you can drill into TCP streams or filter by them. In any case, it is an excellent tool for visualizing tcpdump outputs or capturing your own in a gui interface. ![]() Previously it went by the name Ethereal but around 2006 it changed its name. When we talk about Wireshark, we typically refer to a gui version of tcpdump. Wireshark/tsharkĮarlier we mentioned tcpdump. Better yet, names are used which if planned appropriately can help with reading and understanding the rules over viewing subnets and needing to remember what they correlate to. Without this, when creating firewall rules related to multiple subnets, each one of them would have to be a separate rule but with ipsec, groupings can be created to ease the management of this and make it more transparent. It allows you to create groupings of IPs. Ipset is a tool that works alongside the Linux ipfilter Firewall framework. It can be a little overwhelming at times reading the output of tcpdump if you are not using the right filters or know what you're looking at but with a little training and experience it can take you a long way. It is extremely useful in viewing traffic to help validate traffic is arriving or departing as expected as well as the metadata on the packets to try to detect errors. At the simplest level, it allows you to capture traffic on an endpoint and typically either display to the screen or output to a file to review later or parse in another tool. Tcpdump is an amazing tool but simplistic at the same time. On the other hand, UDP is better for packet loss, jitter and latency testing just due to the nature of the command. ![]() Typically for bandwidth testing, you'll choose TCP mode for the testing. The client and server is typically wrapped into one executable so you can have it installed and on the command line indicate which end is the client and which is the server. It supports a multitude of modes and can even test the line for latency and jitter. When it comes to throughput or bandwidth testing, iperf is the de facto tool for the job. ![]() In any case, the route command will allow you to print and change the route table. The default route is typically the only route that is set under most cases but sometimes in the event that the Linux instance in question is a router, it may contain multiple interfaces and routes to each of them. The route command falls more under the configuration category. What is really great about it is it shows the throughput in both directions of each top offender. ![]() What iftop displays is the list of top connections ranked by throughput, so that you can see many of the top offenders chewing through your available bandwidth or throughput. Instead of processes though it does this for network connections. Iftop, as its name implies, does something similar to the top command. Ever wonder if that service or daemon you started such as apache is actually listening on the right ports or any ports? You can use netstat to view that kind of information to help confirm whether the ports are being listened on. For starters it will show you connection tables, which allows you to see which outgoing connections your system is making and also which incoming connections are established. Netstat is a tool that comes with most Linux distributions and has a few use cases.
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