Linux network tips

Set a static IP

On CentOS 7

For this example I ran a virtual machine on VirtualBox and set only one network interface using NAT

1. Edit the config file that manage your network interface. In my case ifcfg-ens33, but to be sure use ip addr show command or nmcli -p dev

   sudo vim /etc/sysconfig/network-scripts/ifcfg-ens33`
   

2. Add the following lines:

   BOOTPROTO=static
   BROADCAST=192.168.1.255
   IPADDR=192.168.1.60
   NETMASK=255.255.255.0
   NETWORK=192.168.1.0
   

3. Restart network service:

   sudo service network restart
   

Another way is to edit the connection using:

nmtui

Which disply a minimum of graphical interface

On Ubuntu 20.04

Here I also used a VM with VBox, with 2 network interfaces:

• enp0s3: NAT interface and dhcp protocol: 10.0.0.0/16 subnet
• enp0s8: Bridge interface: 192.168.0.0/24 subnet

Let's focus on the second

1. Edit the netplan configuration file

   sudo vim /etc/netplan/01-network-manager-all.yaml
   

note: config file name may change depending on your machine

1. Edit the file

   network:
   # 1st interface (NAT)
    ethernets:
      enp0s3:
        dhcp4: true
   
   # 2nd interface (Bridge)
      enp0s8:
        addresses: [192.168.0.10/24]
        gateway4: 192.168.0.254
        nameservers:
          addresses: [8.8.8.8, 8.8.8.4]
        dhcp4: false
        dhcp6: false
   

Apply modification and restart service

sudo netplan apply
systemctl restart systemd-networkd

Route management

Show all route:

route -n

Change default gateway:

route add default gw 192.168.1.254 eth0

Add a Host to Host route:

route add -host 192.168.1.10 gw 192.168.xx.xx

Add subnet:

route add -net 192.168.1.0 netmask 255.255.255.0 gw 192.168.xx.xx

nmap is very useful tool when dealing with network. Basically it scans interface and you may need to use it carefully and only on your machine. See documentation here use it to scan your whole LAN

nmap -sP 192.168.1.0/24

Configure a proxy

In your bashrc

1. Edit your bashrc file:

   vim ~/.bashrc
   

2. Add the following variable:

   http_proxy="http://<user>:<password>@<proxy_addr>:<proxy_port>
   https_proxy="https://<user>:<password>@<proxy_addr>:<proxy_port>
   no_proxy="localhost, 192.168.*.*"
   

For apt

Note: for centos go to yum instead of apt

1. Edit or create if absent:

   sudo vim /etc/apt/apt.conf
   

2. Add the following lines:

   Acquire::http::Proxy "http://<adress_proxy>:<port>";
   Acquire::https::Proxy "https://<adress_proxy>:<port>";