CKA Networking

Question 1

How can you connect two hosts?

Answer 1

First you need a switch and, physical or virtual interfaces on the host, depending on the host

Question 1

ip link

Answer 1

The command to see the network interfaces on a host

Question 2

What do
ip addr add 192.168.1.10/24 dev eth0
ip addr add 192.168.1.11/24 dev eth0
do?

Answer 2

The command to assign IP addresses to hosts in a network with IP
192.168.1.0

Question 3

How do two small networks with a switch in each of them talk to each other?

Answer 3

You need a router for that.
The router gets 1 IP from each network.

Question 4

How do the devices on the network know which one is the router and they have to use it for communication with the other network?

Answer 4

Type “route” command
You will see the Kernel IP Routing Table
If there is no gateway there, your host does not know where the door is.

To configure gateway, you type

ip route add 192.168.2.0/24 via 192.168.1.1
This means for every host in the 192.168.2.0/24 network, use 192.168.1.1 as gateway (Which is my router’s IP in my network in this scenario)

You have to do this for all the hosts in the network.

Also, to direct every request outside of my network, we can simply say: use this router for every request outside of my network, internet, etc.

ip route add default via 192.168.2.1

If you see 0.0.0.0 in the gateway column, it means that destination is within our network and I don’t need a router.

These changes will not persist, so we need to set them in /etc/network/interfaces file.

Question 5

What does these commands do?
ip link
ip addr
ip addr add
ip route or route
ip route add

Question 6

How do you tell host A that a host named “hebele” is at IP 192.168.1.1?

Answer 6

You add it to /etc/hosts file
This is called name resolution

Question 7

Where does the DNS server address stored in hosts?

Answer 7

In /etc/resolv.conf file
It first checks /etc/hosts file, if the name to resolve is not there, it checks the DNS server.

Question 8

How do I query my DNS server for a specific domain?

Answer 8

nslookup www.google.com
This never checks the /etc/hosts file, always goes to DNS server

Question 9

What other command is handy to test DNS name resolution?

Answer 9

dig www.google.com

Question 10

Which command to create network namespace?

Answer 10

ip netns add red
ip netns add blue

Then check them with ip netns

Question 11

How to check network interfaces in my network namespace?

Answer 11

For this, we need to run “ip link”, the command to list network interfaces within the network interface

ip netns exec red ip link

Same applies with arp tables and routing tables

Question 12

How do you see arp tables?

Answer 12

arp

Question 13

How do you see routing tables?

Answer 13

route

Question 14

How do you list network interfaces?

Answer 14

ip link

Question 15

What does IPAM stand for?

Answer 15

IP Address Management

Question 16

How can you inspect kubelet service?

Answer 16

ps -aux | grep -i kubelet
(it is a process)

Question 17

For kubernetes control plane, what is the path configured with all binaries of CNI supported plugins?

Answer 17

/etc/cni/bin

Question 18

How can you check which CNI plugin is configured on a kubernetes cluster?

Answer 18

ls /etc/cni/net.d/
This is going to tell us which CNI plugin is configured
And if you cat that file, you will see more details

Question 19

What is kubelet responsible for?

Answer 19

Creating pods. It is a process on each node and it watches kube-apiserver for the cluster.

Question 20

What is kube-proxy responsible for?

Answer 20

Creating services. kube-proxy also watches kube-apiserver for clusterwide changes.
Whenever a new service is created, kube-proxy assigns an IP address from a predefined range. kube-proxy creates forwarding rules (like IP address of service 10.99.13.178:80 is forwarded to this pod 10.244.1.2) in each node.
kube-proxy uses 3 different modes for that:
- userspace
- iptables
- ipvs
If not configured, it defaults to iptables.

Question 21

How is DNS resolution handled with the cluster, between pods and services?

Answer 21

By default, kubernetes providers its DNS solution (kube-dns / coredns)
But if you are setting up kubernetes manually, you need to install this.

Question 22

How does Kubernetes implement DNS?

Answer 22

Before k8s 1.12 versions, kubernetes deployed kube-dns but with 1.13, the recommended DNS solution is CoreDNS.
CoreDNS deploys 2 pods, and these pods run coredns executable. It also deploys one service called kube-dns that makes the DNS server reachable across the cluster, by all the pods.

cat /etc/coredns/Corefile

In this file, you can see different plugins (errors, health etc) for handling errors etc.
The same file is passed to the pod in a configmap object. So if you need to modify it, you can use this configmap: kubectl get configmap -n kubesystem —-> coredns

Question 23

How to check kubelet configuration?

Answer 23

cat /var/lib/kubelet/config.yaml