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Network configuration examples on Debian 11 and 12.
Tried to be as thorough much as possible: single nic, multi nics, multi networks, nic bonding.
Debian and Ubuntu network configurations are very different so there are different tutorials for Debian and Ubuntu.
Debian 11 & 12 use ifupdown for network configuration.
Main configuration file is /etc/network/interfaces. This file includes all the files in /etc/network/interfaces.d/ dir.
It is a good practice to keep /etc/network/interfaces as below and create a config file for each nic in /etc/network/interfaces.d/ dir.
sudo nano /etc/network/interfaces
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).
source /etc/network/interfaces.d/*
#
# The loopback network interface
auto lo
iface lo inet loopback
Name server configuration file is /etc/resolv.conf. It can be as simple as below:
nameserver 192.168.1.1
Or may have some detailed configuration as below:
# /etc/resolv.conf
# Primary DNS server
nameserver 8.8.8.8
# Secondary DNS server
nameserver 8.8.4.4
# Tertiary DNS server (optional)
#nameserver 1.1.1.1
# Search domains (optional)
# If a domain name is provided without a fully qualified domain name (FQDN),
# the system appends these search domains to the provided domain to perform
# DNS lookups.
# For example, if "example.com" is provided in a lookup, and "search
# localdomain" is configured, the system will also try to resolve
# example.com.localdomain".
search localdomain
Stop a nic
sudo ifdown enp0s3
Start a nic
sudo ifup enp0s3
To restart a nic, stop it and start it again
sudo ifdown enp0s3
sudo ifup enp0s3
Restart networking (restart all nics and other networking software)
sudo systemctl restart networking
https://www.mybluelinux.com/debian-permanent-static-routes/
https://wiki.debian.org/NetworkConfiguration
https://www.debian.org/doc/manuals/debian-handbook/sect.network-config
ChatGPT
Our nic is enp0s3
sudo nano /etc/network/interfaces.d/enp0s3
Fill as below:
auto enp0s3
iface enp0s3 inet dhcp
Restart networking:
sudo systemctl restart networking
Our nic is enp0s3
sudo nano /etc/network/interfaces.d/enp0s3
Fill as below:
auto enp0s3
iface enp0s3 inet static
address 192.168.1.196/24
broadcast 192.168.1.255
network 192.168.1.0
gateway 192.168.1.1
sudo systemctl restart networking
Our nic is enp0s3
sudo nano /etc/network/interfaces.d/enp0s3
Fill as below:
auto enp0s3
iface enp0s3 inet static
address 192.168.1.196/24
broadcast 192.168.1.255
network 192.168.1.0
gateway 192.168.1.1
iface enp0s3 inet static
address 10.1.1.1/8
sudo systemctl restart networking
Our nics are enp0s3 enp0s8
First nic:
sudo nano /etc/network/interfaces.d/enp0s3
Fill as below:
auto enp0s3
iface enp0s3 inet static
address 192.168.1.196/24
broadcast 192.168.1.255
network 192.168.1.0
gateway 192.168.1.1
Second nic:
sudo nano /etc/network/interfaces.d/enp0s8
Fill as below:
auto enp0s8
iface enp0s8 inet static
address 10.1.1.1/8
broadcast 10.255.255.255
network 10.0.0.0
Restart networking:
sudo systemctl restart networking
We have 2 separate networks (192.168.1.X and 10.X.X.X). Some hosts from one network need to reach to the hosts from the other network.
We are going to install a new host to act as a router between the networks.
The host will have 2 NICs (1 in each network), and we'll enable ip routing on it.
This way, hosts in one network could be able to reach to the hosts in the other network. This will be possible by defining ip routes on the hosts to use the server with 2 nics as a router to the other network.
Hosts in 192.168.1.X network use 192.168.1.1 as the default gateway, hosts in 10.X.X.X network use 10.1.1.1 as the default gateway.
Our router will have 2 NICs, one with the IP 192.168.1.196 and the other with the IP 10.1.1.196.
The hosts in 192.168.1.X network will use 192.168.1.196 to reach the 10.X.X.X network. The hosts in 10.X.X.X network will use 10.1.1.196 to reach the 192.168.1.X network.
We are going to configure the router (192.168.1.196 & 10.1.1.196), the host in the first network (192.168.1.197), and the host in the second network (10.1.1.198), and check connectivity between them.
We have 2 NICs (enp0s3 - 192.168.1.X network, and enp0s8 -10.X.X.X network).
Clean /etc/network/interfaces file
sudo nano /etc/network/interfaces
Set as below
source /etc/network/interfaces.d/*
auto lo
iface lo inet loopback
Configure NICs
(enp0s3): 192.168.1.196/24
sudo nano /etc/network/interfaces.d/enp0s3
Fill as below:
auto enp0s3
iface enp0s3 inet static
address 192.168.1.196/24
broadcast 192.168.1.255
network 192.168.1.0
gateway 192.168.1.1
(enp0s8): 10.1.1.196/8
sudo nano /etc/network/interfaces.d/enp0s8
Fill as below:
auto enp0s8
iface enp0s8 inet static
address 10.1.1.196/8
broadcast 10.255.255.255
network 10.0.0.0
Restart Networking (Your SSH connection may break, reconnect)
sudo systemctl restart networking
Enable IP Forwarding
sudo nano /etc/sysctl.conf
Add the following line to the end
net.ipv4.ip_forward = 1
Activate
sudo sysctl -p
Set Name Server (if not already)
sudo nano /etc/resolv.conf
nameserver 8.8.8.8
nameserver 8.8.4.4
We have 1 NIC (enp0s3 - 192.168.1.X network).
Clear /etc/network/interfaces file
sudo nano /etc/network/interfaces
Set as below
source /etc/network/interfaces.d/*
auto lo
iface lo inet loopback
Configure NIC
(enp0s3): 192.168.1.197/24
sudo nano /etc/network/interfaces.d/enp0s3
auto enp0s3
iface enp0s3 inet static
address 192.168.1.197/24
broadcast 192.168.1.255
network 192.168.1.0
gateway 192.168.1.1
Define Route
Create a script file to add the route when the interface becomes up
sudo nano /etc/network/if-up.d/routes
Fill as below
#!/bin/sh
if [ "$IFACE" = "enp0s3" ]; then
ip route del 10.0.0.0/8 via 192.168.1.196 dev enp0s3
ip route add 10.0.0.0/8 via 192.168.1.196 dev enp0s3
fi
Make the script executable
sudo chmod 750 /etc/network/if-up.d/routes
Restart Networking (Your SSH connection may break, reconnect)
sudo systemctl restart networking
Set Name Server (if not already)
sudo nano /etc/resolv.conf
nameserver 8.8.8.8
nameserver 8.8.4.4
We have 1 NIC (enp0s3 - 10.X.X.X network).
Clear /etc/network/interfaces file
sudo nano /etc/network/interfaces
Set as below
source /etc/network/interfaces.d/*
auto lo
iface lo inet loopback
Configure NIC
(enp0s3): 10.1.1.198/8
sudo nano /etc/network/interfaces.d/enp0s3
auto enp0s3
iface enp0s3 inet static
address 10.1.1.198/8
broadcast 10.255.255.255
network 10.0.0.0
gateway 10.1.1.1
Define Route
Create a script file to add the route when the interface becomes up
sudo nano /etc/network/if-up.d/routes
Fill as below
#!/bin/sh
if [ "$IFACE" = "enp0s3" ]; then
ip route del 192.168.1.0/24 via 10.1.1.196 dev enp0s3
ip route add 192.168.1.0/24 via 10.1.1.196 dev enp0s3
fi
Make the script executable
sudo chmod 750 /etc/network/if-up.d/routes
Restart Networking (Your SSH connection may break, reconnect)
sudo systemctl restart networking
Set Name Servers (if not already)
sudo nano /etc/resolv.conf
nameserver 8.8.8.8
nameserver 8.8.4.4
The host in the first network can ping the host in the other network now, and vice versa.
Try on the first host (192.168.1.197)
ping 10.1.1.198
Try on the second host (10.1.1.198)
ping 192.168.1.197
For a host to connect to another host on the other network, routing must be defined on the both hosts.
Network interface card bonding simply means using 2 (or more) NICs together to achive redundancy and/or increased throughput.
There are many types of bonding, some most useds are:
Active Backup: Also known as failover mode. In this mode, one interface is active while the other interfaces remain in standby mode. If the active interface fails, one of the standby interfaces takes over. It provides redundancy but does not offer load balancing.
Balance-rr (Round-Robin): Packets are transmitted sequentially across the bonded interfaces in a round-robin fashion. Provides load balancing and increased throughput, but it does not provide fault tolerance.
Balance-xor: Combines the MAC addresses of the interfaces and applies an XOR operation to determine the outgoing interface. It provides load balancing and fault tolerance, but it requires switch support for optimal performance.
Broadcast: All packets are sent on all interfaces. It's typically used in situations where the switch does not support any of the other bonding modes. It doesn't provide load balancing but offers fault tolerance.
To use NIC bonding, ifenslave package must be installed:
sudo apt update
sudo apt install ifenslave
All of our examples will have 2 nics (enp0s3 and enp0s8) in the same network (192.168.1.X)
Install ifenslave package (if not installed already)
sudo apt update
sudo apt install ifenslave -y
Ensure bonding kernel module is loaded
sudo modprobe bonding
Ensure loading kernel module at the startup
sudo nano /etc/modules
Add to the end of the file (if it does not exist)
bonding
Clear /etc/network/interfaces file
sudo nano /etc/network/interfaces
Set as below:
source /etc/network/interfaces.d/*
auto lo
iface lo inet loopback
Configure the bond
sudo nano /etc/network/interfaces.d/bond
Fill as below:
auto enp0s3
iface enp0s3 inet manual
bond-master bond0
auto enp0s8
iface enp0s8 inet manual
bond-master bond0
auto bond0
iface bond0 inet static
address 192.168.1.196/24
netmask 255.255.255.0
network 192.168.1.0
gateway 192.168.1.1
slaves enp0s3 enp0s8
bond-mode active-backup
bond-primary enp0s3
Restart Networking
sudo systemctl restart networking
Set Name Servers (if not already)
sudo nano /etc/resolv.conf
nameserver 8.8.8.8
nameserver 8.8.4.4
Check the status of the bond
sudo cat /proc/net/bonding/bond0
Install ifenslave package (if not installed already)
sudo apt update
sudo apt install ifenslave -y
Ensure bonding kernel module is loaded
sudo modprobe bonding
Ensure loading kernel module at the startup
sudo nano /etc/modules
Add to the end of the file (if it does not exist)
bonding
Clear /etc/network/interfaces file
sudo nano /etc/network/interfaces
Set as below:
source /etc/network/interfaces.d/*
auto lo
iface lo inet loopback
Configure the bond
sudo nano /etc/network/interfaces.d/bond
auto enp0s3
iface enp0s3 inet manual
bond-master bond0
auto enp0s8
iface enp0s8 inet manual
bond-master bond0
auto bond0
iface bond0 inet static
address 192.168.1.196/24
netmask 255.255.255.0
network 192.168.1.0
gateway 192.168.1.1
bond-slaves enp0s3 enp0s8
bond-mode balance-rr
Restart Networking
sudo systemctl restart networking
Check the status of the bond
sudo cat /proc/net/bonding/bond0
Install ifenslave package (if not installed already)
sudo apt update
sudo apt install ifenslave -y
Ensure bonding kernel module is loaded
sudo modprobe bonding
Ensure loading kernel module at the startup
sudo nano /etc/modules
Add to the end of the file (if it does not exist)
bonding
Clear /etc/network/interfaces file
sudo nano /etc/network/interfaces
Set as below
source /etc/network/interfaces.d/*
auto lo
iface lo inet loopback
Configure the bond
sudo nano /etc/network/interfaces.d/bond
auto enp0s3
iface enp0s3 inet manual
bond-master bond0
auto enp0s8
iface enp0s8 inet manual
bond-master bond0
auto bond0
iface bond0 inet static
address 192.168.1.196/24
netmask 255.255.255.0
network 192.168.1.0
gateway 192.168.1.1
bond-slaves enp0s3 enp0s8
bond-mode balance-xor
Restart Networking
sudo systemctl restart networking
Check the status of the bond
sudo cat /proc/net/bonding/bond0
Install ifenslave package (if not installed already)
sudo apt update
sudo apt install ifenslave -y
Ensure bonding kernel module is loaded
sudo modprobe bonding
Ensure loading kernel module at the startup
sudo nano /etc/modules
Add to the end of the file (if it does not exist)
bonding
Clear /etc/network/interfaces file
sudo nano /etc/network/interfaces
Set as below
source /etc/network/interfaces.d/*
auto lo
iface lo inet loopback
Configure the bond
sudo nano /etc/network/interfaces.d/bond
auto enp0s3
iface enp0s3 inet manual
bond-master bond0
auto enp0s8
iface enp0s8 inet manual
bond-master bond0
auto bond0
iface bond0 inet static
address 192.168.1.196/24
netmask 255.255.255.0
network 192.168.1.0
gateway 192.168.1.1
bond-slaves enp0s3 enp0s8
bond-mode broadcast
Restart Networking
sudo systemctl restart networking
Check the status of the bond
sudo cat /proc/net/bonding/bond0