VMware ESXi and vSphere Cluster Management

Linux ifconfig Command: View and Configure Network Interfaces

Learn how to use the legacy Linux ifconfig command to inspect interfaces, read addresses and flags, assign a temporary IPv4 address, and enable or disable devices.

What is ifconfig?

ifconfig is a command-line utility for examining and changing Linux network interfaces. It is traditionally provided by the net-tools package.

A network interface is a communication endpoint provided by a physical adapter, virtual device, wireless adapter, VLAN, or the special loopback device. Historically, administrators used ifconfig for two main tasks:

• Displaying the status and addressing information of interfaces.
• Changing interface parameters such as an IPv4 address, netmask, and administrative state.

Modern Linux distributions generally recommend the ip command from the iproute2 suite. However, ifconfig remains useful on older systems and when working with older documentation or scripts.

List active network interfaces

Run ifconfig without an interface name to display interfaces that are currently active:

ifconfig

The output normally contains one section for each active interface. An administratively down interface may be omitted by some ifconfig implementations. To include inactive interfaces, use the -a option:

ifconfig -a

The exact formatting varies between systems, but common output includes the interface name, addresses, hardware address, state flags, MTU, and traffic counters.

Common interface names

• eth0 is a traditional name for the first Ethernet interface.
• enp0s3 and ens33 are examples of predictable names used by many modern Linux systems. The name is based on hardware or firmware location rather than simply being numbered.
• lo is the loopback interface. It supports communication from a host to itself and is not an external network adapter.

A physical or virtual adapter connects the host to another network or service. The loopback device instead keeps traffic inside the same operating system. Applications commonly use it for local services, often with an address in the 127.0.0.0/8 range.

View one interface

To limit the output to one named interface, place its name after the command:

ifconfig eth0

Replace eth0 with the actual device name on your system, such as enp0s3, ens33, a wireless name, or a virtual interface. Discover names with:

ifconfig -a

You can inspect the loopback interface separately:

ifconfig lo

Read ifconfig output

An IPv4 address is a 32-bit network-layer address commonly written in dotted-decimal form, such as 192.0.2.10. A netmask separates the network portion of that address from the host portion. The address 192.0.2.10 with netmask 255.255.255.0 is equivalent to the prefix notation 192.0.2.10/24: the first 24 bits identify the network and the remaining 8 bits identify a host within it.

An IPv6 address may appear when IPv6 is configured. A broadcast address identifies all hosts on a local IPv4 subnet where broadcast is supported. A MAC address is a link-layer identifier associated with the interface. Unlike an IP address, it identifies the interface at the data-link layer and is used for local network delivery.

Temporarily assign an IPv4 address

Use this syntax to assign an IPv4 address and netmask:

sudo ifconfig <interface> <ipv4-address> netmask <netmask>

For example, this uses 192.0.2.10, an address reserved for documentation:

sudo ifconfig eth0 192.0.2.10 netmask 255.255.255.0

Verify the result by inspecting the interface:

ifconfig eth0

Direct changes made with ifconfig are normally temporary. They can disappear after a reboot, a network service restart, a DHCP renewal, or an action by NetworkManager or another network manager. Changing an active interface over SSH can also terminate your current session.

Enable or disable an interface

Bring an interface administratively up with:

sudo ifconfig eth0 up

Disable it with:

sudo ifconfig eth0 down

down disables network traffic on the device. up re-enables its administrative state. An interface can be administratively enabled without having a working carrier: for example, an Ethernet cable may be disconnected, or a wireless adapter may not be associated with an access point. The UP and RUNNING flags help distinguish these conditions, although detailed link information is often clearer with ip link show.

Privileges and persistent configuration

Reading interface information usually works as a regular user, but changing addresses or interface state requires elevated privileges:

sudo ifconfig <interface> up
sudo ifconfig <interface> 192.0.2.10 netmask 255.255.255.0

There is an important difference between a temporary command-line adjustment and persistent network configuration:

For permanent settings, use the supported method for your distribution, such as NetworkManager, systemd-networkd, Netplan, or traditional distribution-specific network scripts. Avoid having multiple network managers compete to control the same interface.

Modern equivalents with ip

The ip command from iproute2 is the recommended tool for current Linux administration. These commands cover the most common ifconfig tasks:

The ip commands also make the distinction between address information and link information explicit: use ip addr for addresses and ip link for device and link state.

Troubleshooting

ifconfig: command not found

The net-tools package may not be installed, or the distribution may expect administrators to use iproute2. Use the modern commands where possible:

ip addr show
ip link show

Install the distribution's net-tools package only when legacy compatibility is required, using the package manager and procedures supported by that distribution.

The expected eth0 interface does not exist

Modern predictable naming may produce a name such as enp0s3 or ens33. The machine may also have only a wireless, virtual, or differently named adapter. Run:

ifconfig -a
ip link show

Replace eth0 in examples with the real interface name.

The configured address disappears

A direct ifconfig change is temporary, or DHCP, NetworkManager, or another service may have replaced it. Check whether DHCP is intended to manage the interface and configure the address through the distribution-supported persistent network system.

Network access stops after using down

The selected interface was administratively disabled. Restore it with:

sudo ifconfig <interface> up

If you disabled the remote management interface, use a local console, out-of-band management, or an alternate connection.

The interface is UP but traffic fails

An enabled interface may still lack physical carrier or wireless association. Addressing, netmask, route, gateway, VLAN, DNS, or firewall problems can also prevent communication. Inspect the relevant layers:

ip link show
ip addr show
ip route show

Check local gateway reachability before investigating DNS. The RUNNING flag is useful, but it does not prove that every part of the network configuration is correct.

Permission denied or operation not permitted

Changing interface state or addresses requires elevated privileges. Retry with sudo and confirm that your account is authorized to perform administrative operations.

Key points

• ifconfig is a legacy net-tools utility for viewing and changing network-interface settings.
• ifconfig lists active interfaces; ifconfig -a includes interfaces that may be administratively down.
• Interface names may be traditional, such as eth0, or predictable, such as enp0s3 and ens33.
• lo is the host-local loopback interface, not an external network adapter.
• IPv4 addresses, netmasks, broadcast addresses, MAC addresses, flags, MTU values, and counters describe different aspects of an interface.
• Direct ifconfig changes are normally temporary and can interrupt remote administration.
• Use ip addr and ip link for modern Linux administration, and use a supported network manager for persistent settings.

For more practice with the legacy utility, return to the Linux ifconfig command guide and compare each task with its modern ip equivalent.