linuxexpert-practice-labs/labs/linux-plus/1-4-2-network-tools/README.md

Linux+ 1.4.2: Network tools

Mapping the VM's network, following a lookup and a connection, capturing DNS traffic, and testing a port and throughput between two machines.

Before you start

The peer, at 10.99.0.2 (name peer), stands in for the other VM. It sits on this VM's second network, 10.99.0.0/24, where this VM is 10.99.0.1. It shares this VM's files and installed programs, but has its own network stack: get a shell there with sudo ip netns exec lepeer bash. Tasks 1 and 2 ask for findings: write them to the files in /root/lab-answers/ that they name. Task 2 needs internet access. Reset closes the ports again and removes iperf3 and nc if they weren't installed before the lab.

Tasks

1. Map this VM's network: addresses, routes, neighbors, listening ports. Write the address of the default gateway to /root/lab-answers/1.
2. Look up www.kernel.org, trace the path to it, and fetch the headers of https://www.kernel.org. Write the first line of the headers (the status line, such as HTTP/1.1 301 Moved Permanently) to /root/lab-answers/2.
3. Capture your own DNS traffic with tcpdump while you look up a name. Not graded.
4. Test a port and the throughput between this VM (VM A) and the peer (VM B). Install iperf3 and nc, and if a firewall is running here, open ports 9000/tcp and 5201/tcp until the next reboot. Run nc -l 9000 here and nc -zv 10.99.0.1 9000 in the peer, then iperf3 -s here and iperf3 -c 10.99.0.1 in the peer.

Hints

• ip -br a, ip r, ip neigh, ss -tulnp, hostname -I.
• On the RHEL family, dig is in bind-utils, and nc in nmap-ncat. dig +short, tracepath -n, curl -sI URL | head -1.
• tcpdump -i any -nn port 53 in one terminal, dig example.org in another; Ctrl+c stops tcpdump.
• firewall-cmd --add-port=9000/tcp --add-port=5201/tcp (without --permanent); with ufw, ufw allow 9000/tcp.