linuxexpert-practice-labs/labs/linux-plus/5-3-2-addressing-routing-dns-issues

Linux+ 5.3.2: Addressing, routing and DNS problems

Working through the layers: the route a packet takes, a missing default route, and a name that resolves to the wrong address.

Before you start

The peer, at 10.99.0.2 (name peer), is another machine on this VM's second network, 10.99.0.0/24; this VM, 10.99.0.1, is its gateway. Get a shell there with sudo ip netns exec lepeer bash. From the peer, 198.51.100.9 stands in for an internet address such as 9.9.9.9. The peer reads its network settings at boot from /etc/netns/lepeer/network (ip -batch commands), so fix that file as well as the running system. The lab has also changed something on this VM. Task 3 needs the internet. Write answers to the files in /root/lab-answers/.

Tasks

1. Walk the method on this VM: addresses, routes, the gateway, an internet address, a name, a port. Write the gateway address and the interface this VM uses to reach 9.9.9.9 to /root/lab-answers/1.
2. The peer can't reach 198.51.100.9. Find out why from the error, and fix it, now and at boot.
3. On this VM, www.kernel.org resolves to a wrong address for most programs, but dig gets the right one. Find out where the wrong address comes from, write that source to /root/lab-answers/3, and fix it.
4. Compare IPv4 and IPv6 to www.kernel.org (dig AAAA, curl -4, curl -6). Not graded.

Hints

• ip -br addr, ip route, ip route get 9.9.9.9, ping, getent hosts, nc -zv.
• "Network is unreachable" means no route; ip route add default via. Lines in the peer's file are ip commands without the ip.
• getent hosts follows /etc/nsswitch.conf; dig asks the DNS server only (dnf install bind-utils or apt install dnsutils if it's missing).