Linux Networking Basics: ifconfig, ip, and netstat

Checking Network Interfaces with ifconfig

ifconfig is part of the net-tools package (deprecated but still common).

# install net-tools if missing
sudo apt install net-tools   # Ubuntu/Debian
sudo dnf install net-tools   # CentOS/AlmaLinux

# show all network interfaces
ifconfig -a

# bring interface up or down
sudo ifconfig eth0 up
sudo ifconfig eth0 down

Using the ip Command (Modern Replacement)

The ip command (from iproute2) is the modern tool for networking.

# show all interfaces and IP addresses
ip a

# show routing table
ip route

# assign a new IP temporarily
sudo ip addr add 192.168.1.50/24 dev eth0

# remove assigned IP
sudo ip addr del 192.168.1.50/24 dev eth0

# bring interface up/down
sudo ip link set eth0 up
sudo ip link set eth0 down

Monitoring Connections with netstat

netstat shows open ports, routing, and connections.

# show all listening ports
netstat -tuln

# show active connections
netstat -antp

# show routing table
netstat -r

On newer systems, use ss as a faster replacement:

# show all listening sockets
ss -tuln

# show active TCP connections
ss -ant

Testing Connectivity

# ping an address
ping -c 4 google.com

# traceroute to a host
traceroute 8.8.8.8     # may need: sudo apt install traceroute

# check DNS resolution
dig example.com
host example.com

Best Practices

• Use ip instead of ifconfig for modern setups.
• Prefer ss over netstat for better performance.
• Make network config persistent by editing:
  • Ubuntu/Debian: /etc/netplan/
  • CentOS/AlmaLinux: /etc/sysconfig/network-scripts/