Change DNS nameservers using NetworkManager
sudo nmcli connection modify <connection name> ipv4.dns "1.1.1.1 8.8.8.8"
Apply changes:
sudo nmcli dev reapply <interface>
network/
How to reload the connection with NetworkManager
Reload interface configuration:
sudo nmcli connection reload
This command will ONLY make NetworkManager aware of new configuration changes. To apply the new changes, run the following command:
sudo nmcli dev reapply <interface>
Connect dedicated servers with cloud servers in hetzner via vSwitch
Main article is provided by Hetzner team here. This article contains instructions for creating vlan interface in Centos 8 using nmcli.
Assumptions (same us in the main article + listed below):
- VLAN ID is
4001 - parent network interface is
enp195s0
Steps:
- Create new connection:
nmcli connection add type vlan con-name vlan4001 ifname vlan4001 vlan.parent enp195s0 vlan.id 4001
- Configure the connection:
nmcli connection modify vlan4001 802-3-ethernet.mtu 1400
nmcli connection modify vlan4001 ipv4.addresses '10.0.1.2/24'
nmcli connection modify vlan4001 ipv4.gateway '10.0.1.1'
nmcli connection modify vlan4001 ipv4.dns '10.0.0.4' # (optional)
nmcli connection modify vlan4001 ipv4.method manual
nmcli connection modify vlan4001 +ipv4.routes "10.0.0.0/16 10.0.1.1"
- Restart the connection
nmcli connection down vlan4001
nmcli connection up vlan4001
- Verify configuration
# Prints what gateway is used to reach the ip
ip route get 10.0.0.5
# Print all connection information
nmcli connection show vlan4001
# Print routing table
ip r
# Use tui interface for NetworkManager
dnf install NetworkManager-tui
nmtui
Restarting NetworkManager wasn’t enough to apply custom routes. Bring interface up and down
And the link to the great RedHat documentation
netcat example
Listen on specified port:
nc -l -v -k 8888
Connect via netcat:
nc -v google.com 80
Extract and count IP addresses from logs
journalctl -n 1000 | grep -E -o "([0-9]{1,3}[\.]){3}[0-9]{1,3}" | sort | uniq -c
Debug route table
List all routes in system:
route -n
Get route for a specific IP:
ip route get 1.1.1.1
Wait until able to connect
while ! nc -w5 -z 10.0.0.100 22; do echo "hello"; done
Check and modify mtu of a connection
To check:
[root@lxd-node3 ~]# netstat -i
Kernel Interface table
Iface MTU RX-OK RX-ERR RX-DRP RX-OVR TX-OK TX-ERR TX-DRP TX-OVR Flg
ens10 1450 455 0 0 0 671 0 0 0 BMRU
eth0 1500 28 0 0 0 32 0 0 0 BMRU
lo 65536 0 0 0 0 0 0 0 0 LRU
Modify temporarily:
ifconfig eth0 mtu 1450
Permanently: edit /etc/sysconfig/network-scripts/ifcfg-eth0 file and add:
MTU=1450
Might be the reason why the system can establish HTTP connection but HTTPS
Useful wifi commands
List used wifi frequencies
sudo iwlist wlp1s0 scan | grep Frequency | sort | uniq -c | sort -n
List available channels
iwlist channel
List wifi networks
nmcli d wifi
List all IP addresses in a network
To list ip addresses of all connected to the network devices, use this command:
nmap -sn 192.168.0.0/24