ifconfig – configure network interfaces (legacy)
ifconfig displays and configures network interfaces. On modern Linux, use ip instead; ifconfig remains common on macOS and BSD.
Synopsis
ifconfig [INTERFACE] [OPTIONS]
Examples
Show all interfaces
$ ifconfig
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.1.100 netmask 255.255.255.0 broadcast 192.168.1.255
ether 52:54:00:12:34:56 txqueuelen 1000 (Ethernet)
RX packets 12345 bytes 1234567 (1.2 MB)
TX packets 6789 bytes 567890 (567.8 KB)
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
Show specific interface
$ ifconfig eth0
$ ifconfig en0 # macOS
Show all including down
$ ifconfig -a
Configuration (require root)
Assign IP address
$ sudo ifconfig eth0 192.168.1.100 netmask 255.255.255.0
Bring interface up/down
$ sudo ifconfig eth0 up
$ sudo ifconfig eth0 down
Set MTU
$ sudo ifconfig eth0 mtu 9000
Enable promiscuous mode
$ sudo ifconfig eth0 promisc
$ sudo ifconfig eth0 -promisc
Common Output Fields
| Field | Meaning |
|---|---|
| inet | IPv4 address |
| inet6 | IPv6 address |
| netmask | Subnet mask |
| broadcast | Broadcast address |
| ether | MAC address |
| RX/TX | Received/transmitted packets |
| mtu | Maximum transmission unit |
ifconfig vs ip
On Linux, prefer ip:
# Show addresses
ifconfig → ip addr
ifconfig eth0 → ip addr show eth0
# Set address
ifconfig eth0 192.168.1.100 → ip addr add 192.168.1.100/24 dev eth0
# Interface up
ifconfig eth0 up → ip link set eth0 up
Tips
- Not installed by default: On minimal Linux, install
net-tools - Use ip on Linux: ifconfig is deprecated
- macOS/BSD: ifconfig is still standard
- Changes are temporary: Use system network config for permanent changes
