[CKA] 011. Network

Network concepts and configurations relevant to Kubernetes clusters.

Network Basic

Switch : A PC (192.168.1.10) -> Switch (192.168.1.0) -> B PC (192.168.1.11)
Router : Switch (192.168.1.0) <-> Switch (192.168.2.0)
Gateway : Role of Router
routing table : destination -> gateway
ip link : network cards list
ip addr : logical address info list
ip addr add 192.168.1.10/24 dev eth0 : logical address apply
ip route or route : check route info
ip route add 192.68.1.0/24 via 192.168,.2.1 : add route rule
cat /proc/sys/net/ipv4/ip_forward : route of os setting
- 0 (disable)
- 1 (enable)
DNS
- Once upon a time, /etc/hosts is written for name resolution
- /etc/resolv.conf : all pc use this file for dns server info
- Over Time DNS server is used for name resolution
```
cat /etc/hosts
nameserver  192.168.1.100
search      mydomain.com
```
  - if need dns server and hosts order is /etc/nsswitch.conf
- public dns: www.google.com -> use public dns server like 8.8.8.8
- dns Server save for using record type
- nslookup : nslookup google.com 8.8.8.8 -> google’s ip from 8.8.8.8
- dig : more detailed info than nslookup

Linux kernel support
Logical separation of network
order
- ip netns add red : creating network namespace ‘red’
- ip -n red link : check network namespace ‘red’
- ip link add veth-red type veth peer name veth-blue : create virtual caple
- ip link set vth-red netns red : move veth-red to red namespace
- ip -n red addr add 192.168.15.1 dev veth-red : assign ip to veth-red (dev : device)
- ip -n red link set veth-red up : start up
order 2
- ip link add v-net-0 type bridge : create bridge
- ip link set veth-red-br master v-net-0 : connect veth-red to bridge
- ip addr add 192.168.15.5/24 dev v-net-0 : assign ip to bridge