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.