7 Manage Basic Networking

# 7.1 Configure Networking and hostname resolution statically of dynamically


To have information about your network adapters
```
$ ip link show
$ ip l
```
To have information about your ip adresses
```
$ ip addresses show
$ ip a
```
View the routing tables
```
$ ip route show
$ ip r
```
View DNS resolvers
```
$ cat /etc/resolv.conf
```

Network configuration settings are defined in:
```
$ ls /etc/sysconfig/network-scripts/
```

Network manager tools
```
$ sudo nmtui
$ sudo nmcli
```
To force network manager to immediately apply changes, rather than reboot
```
$ sudo nmcli device reapply enp0s3

Static hostname resolution
$ sudo vim /etc/hosts
$ sudo hostnamectl
```
Update the transient hostname
$ sudo hostnamectl set-hostname dev-host01

# 7.2 Configure network services to start automatically at boot
```
$ sudo systemctl status NetworkManager.service

If not present, you can install it

$ sudo dnf install NetworkManager

$ sudo systemctl start NetworkManager.service

$ sudo systemctl enable NetworkManager.service
```
To enable a connection to auto start at boot
List the connections, not the <name>
$ nmcli connection show

$ sudo nmcli connection modify <name> autoconnect yes


# 7.3 Start, Stop and Check Network Services

Two utilities : ss and netstat

To see programs ready to accept network connections
```
$ sudo ss -tunlp

$ sudo lsof -p <pid>
```

Netstat uses almost the same arguments as ss



# 7.3 Implement packet filtering

FirewallD manages network interfaces in zones

Default zone is public, any incoming connection is blocked

Check default zone
```
$ sudo firewall-cmd --get-default-zone
```

to change the default zone
```
$ sudo firewall-cmd --set-default-zone=public
```

To see the current firewall rules
```
$ sudo firewall-cmd --list-all
```
To have more information about a service
$ sudo firewall-cmd --info-service=cockpit

Allow traffic to a service
```
$ sudo firewall-cmd --add-service=http
or
$ sudo firewall-cmd --add-port=80/tcp
```
To remove a service from a set of accepted connections
```
$ sudo firewall-cmd --remove-service=http
or
$ sudo firewall-cmd --remove-port=80/tcp
```

In a public zone, the main policy is to deny incomming connections to all ports
To setup a trusted zone
```
$ sudo firewall-cmd --add-source=10.11.12.0/24 --zone=trusted
```
To get a list of zones
```
$ sudo firewall-cmd --get-active-zones
```
To remove a filter based on adresses
```
$ sudo firewall-cmd --remove-source=10.11.12.0/24 --zone=trusted
```
To allow incoming trafic on specific port
```
$ sudo firewall-cmd --add-port=12345/tcp
```

Take a look at all current rules
```
$ sudo firewall-cmd --list-all
```
To make rules permanent/persistent
```
$ sudo firewall-cmd --runtime-to-permanent
or
$ sudo firewall-cmd --add-port=12345/tcp --permanent
```

# 7.4 : Statically route IP traffic

Network 1 : 10.0.0.0
CompA 	  : 10.0.0.1

Network 2 : 192.168.0.0
CompB	  : 192.168.0.1

RouterC : 10.0.0.100, 192.168.0.100

> On CompA, set static route to Network B
```
$ sudo ip route add 192.168.0.0/24 via 10.0.0.100 dev enp0s3
```

> To delete a route
```
$ sudo ip route del 192.168.0.0/24
```
> Add default route(Gateway)
```
$ sudo ip route add default via 10.0.0.100
```
To delete a default route
```
$ sudo ip route del default via 10.0.0.100
```

To make changes permanent
Look at network manager
```
$ nmcli connection show

$ sudo nmcli connection modify enp0s3 +ipv6.routes "192.168.0.0/24 10.0.0.100"

$ sudo nmcli device reapply enp0s3
```
Confirm results
```
$ ip route show
```

>To remove these routes
```
$ sudo nmcli connection modify enp0s3 -ipv6.routes "192.168.0.0/24 10.0.0.100"

$ sudo nmcli device reapply enp0s3
```

If you forget these commands, you can user __nmtui__




# 7.5 Synchronizing time using network clients

The tool used by CentOS is chronyd
To make sure it's currently running
```
$ systemctl status chronyd.service
```

You can also run __timedatectl__
```
$ timedatectl
```

To install/enable chronyd
1. Make sure the time-zone is setup
```
$ sudo timedatectl set-timezone America/New_York
```
	> To see all available time-zones
	  ```
	  $ timedatectl list-timezones
	  ```

2. Install the chrony daemon
```
$ sudo dnf install chrony
```

3. Start it and enable it
```
$ sudo systemctl start chronyd.service

$ sudo systemctl enable chronyd.service
```

4. Check now the time and date control
```
timedatectl
```

5. If NTP synchronization is not enabled, enable it
```
$ sudo systemctl set-ntp true
```