ifconfig Command in Linux

The ifconfig (interface configuration) command is a Linux networking utility used to view and configure network interfaces. It allows administrators to inspect interface details such as IP addresses, MAC addresses, packet statistics and link status.

• Displays network interface details such as IP address, MAC address, MTU and packet statistics
• Allows administrators to enable or disable network interfaces
• Helps in monitoring interface activity and diagnosing network problems
• Can assign IP addresses, netmasks and broadcast addresses
• Part of the net-tools package, commonly used in traditional Linux systems

Example: Finding Your IP Address in Linux

To view information about all network interfaces on your Linux system

Command:

ifconfig

• ifconfig: Without arguments displays all active network interfaces
• Shows important networking information such as IPv4 and IPv6 addresses, MAC address, MTU size, Packet transmission statistics

Output:

Here,

1. eno1 (Wired / Ethernet Network Interface)

eno1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500

• eno1: Your wired LAN (Ethernet) card
• UP: Interface is enabled
• RUNNING: Cable is connected & link is active
• BROADCAST: Can send broadcast packets
• MULTICAST: Supports multicast traffic
• mtu 1500: Maximum data size per packet

Practical use:

• Used when your laptop is connected via LAN cable
• MTU value is important for VPN connections, corporate networks and performance tuning

IPv4 Address Information:

inet 192.168.42.0 netmask 255.255.255.0  broadcast 192.168.42.255

• inet: IPv4 address assigned to the interface
• netmask: Defines network range
• broadcast: Address used to communicate with all devices in the network

Practical use:

• Helps identify which network you are connected to
• Used while configuring routers, DHCP, static IPs

IPv6 Address:

inet6 fe80::4d2c:0edb:a219:acf0

• Automatically assigned IPv6 link-local address

Practical use:

• Required for IPv6 communication
• Common in modern networks, cloud environments and IoT devices

MAC Address:

ether c8:4b:d6:62:bb:da

• Hardware address of the network interface.

Practical use:

• MAC filtering in routers
• Network access control
• Device identification

Packet Statistics:

RX packets / TX packets

• RX (Receive): Data packets received
• TX (Transmit): Data packets sent

Practical use:

• Monitor network traffic usage
• Diagnose network performance issues

Error Indicators:

errors dropped overruns frame

• errors: Packet errors detected
• dropped: Packets discarded
• overruns: Buffer overflow
• frame: Frame alignment errors

Practical use:

• Detect faulty cables
• Identify driver problems
• Diagnose hardware interference

2. lo (Loopback Interface)

lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1

• lo: Loopback interface
• Used for internal system communication
• 127.0.0.1 refers to localhost

Practical use:

• Test services locally
• Run applications or servers on the same machine

3. wlp0s20f3 (Wireless / Wi-Fi Interface)

Wireless network interface used for Wi-Fi connections

wlp0s20f3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>
inet 10.143.75.50

• Your Wi-Fi adapter
• Active and connected

Practical use:

• Provides wireless internet connectivity
• Often used in Kali Linux for wireless penetration testing

Syntax

ifconfig [interface] [options]

• interface: Name of the network interface you want to configure or display information for (e.g., eth0, wlan0).
• options: Various command-line options that can be used to modify the behavior of ifconfig.

Installing ifconfig (net-tools)

Many modern Linux distributions do not include ifconfig by default. If you see the error. You need to install the net-tools package.

For Debian, Ubuntu and related Linux distributions.

Command:

sudo apt install net-tools

For RHEL (Red Hat Enterprise Linux) based Distributions

Command:

dnf install net-tools

Options available in `ifconfig` Command

Public IP Address in Linux

A public IP address is a globally unique identifier assigned to a device that is directly connected to the internet. It enables other devices and services on the internet to locate and communicate with that device. Public IP addresses are assigned by the Internet Assigned Numbers Authority (IANA) through Internet Service Providers (ISPs) and are globally route table across the internet.

Public IPs are commonly required for:

• Web servers and website hosting services
• Cloud servers, APIs and online applications
• Systems that need to be accessed from outside a local network

Example: Viewing the Public IP Address in Linux

Linux systems can retrieve the public IP address by querying external web services using command-line tools.

Command:

curl ifconfig.me

• This command retrieves your public IP address from a web service.

Methods to Display the Public IP Address

1. Using wget with ifconfig.me

Command:

wget -qO- ifconfig.me

Output:

2. Using dig with OpenDNS

This command uses the OpenDNS resolver to query your public IP address.

Command:

dig +short myip.opendns.com @resolver1.opendns.com

Output:

3. Using curl with icanhazip.com

This command queries the icanhazip.com service to obtain your public IP address.

Command:

curl icanhazip.com

Output:

4. Using wget with icanhazip.com

Similar to the curl command, this uses the icanhazip.com service to fetch your public IP address.

Command:

wget -qO- icanhazip.com

Output:

5. Using Google/OpenDNS resolver

This command utilizes the DNS service provided by Google to resolve your public IP address.

Command:

host myip.opendns.com resolver1.opendns.com

Output:

Private IP Address in Linux

A private IP address is used within a local network such as a home, office or organizational intranet. These addresses are not directly accessible from the internet. Private IP addresses are defined by the Internet Engineering Task Force (IETF) in RFC 1918 and are reserved exclusively for internal networking.

Private IP Address Ranges

• 10.0.0.0 – 10.255.255.255 (10.0.0.0/8)
• 172.16.0.0 – 172.31.255.255 (172.16.0.0/12)
• 192.168.0.0 – 192.168.255.255 (192.168.0.0/16)

Devices inside the same private network can communicate directly using these addresses. To access the internet, private IPs rely on Network Address Translation (NAT), which maps them to a shared public IP.

Example: Viewing Private IP Addresses in Linux

Linux provides multiple tools to display private IP addresses assigned to network interfaces.

Command:

ifconfig

or

ip addr

Methods to Display Private IP Addresses

1. Using hostname

The -I option with the hostname command can be used to display the private IP address of your machine.

Command:

hostname -I

Output:

2. Using nmcli (NetworkManager command-line tool)

If you're using NetworkManager, this command filters out IPv4 addresses associated with your network interfaces.

Command:

nmcli dev show | grep IP4.ADDRESS

Output:

3. Using awk with ifconfig

This command uses the awk tool to filter and print only the private IP addresses from the ifconfig output.

Command:

ifconfig | awk '/inet / {print $2}'

Output:

4. Using grep with ip

This command uses grep with Perl-compatible regular expressions to extract private IP addresses from the ip command output.

Command:

ip addr show | grep -oP 'inet \K[\d.]+'

Output:

5. Using ss (socket statistics)

This complex command lists the IP addresses to which the system is listening for incoming connections.

Command:

ss -tunapl | grep LISTEN | awk '{print $5}' | cut -d: -f1 | sort -u

Output:

Linux ifconfig Command Examples

1. Display Specific Network Interface

This command shows detailed information about the specified interface, eth0.

ifconfig eth0

2. Enable a Network Interface

This command activates the specified network interface, eth0.

ifconfig eth0 up

3. Disable a Network Interface

This command deactivates the specified network interface, eth0.

ifconfig eth0 down

4. Assign an IP Address

This command assigns the IP address 192.168.1.10 to the specified network interface, eth0.

ifconfig eth0 192.168.1.10

5. Set a Netmask

This command sets the netmask for the specified network interface, eth0.

ifconfig eth0 netmask 255.255.255.0

6. Set a Broadcast Address

This command sets the broadcast address for the specified network interface, eth0.

ifconfig eth0 broadcast 192.168.1.255

7. Change the MAC Address

This command changes the MAC address of the specified network interface, eth0.

ifconfig eth0 hw ether 00:1a:2b:3c:4d:5e

8. Add an Alias to a Network Interface

This command adds an alias with IP address 192.168.1.20 to the specified network interface, eth0.

ifconfig eth0:0 192.168.1.20

9. Remove an Alias from a Network Interface

This command removes the alias eth0:0 from the specified network interface.

ifconfig eth0:0 down