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How to Check Network Interface in Linux: ip, ifconfig, ethtool

Check network interfaces in Linux with ip link, ip addr, and ethtool — see IP addresses, interface state, link speed, and diagnose interface-level network problems.

April 22, 2026·6 min read·Damon

Network is down. Or you need to know the IP, the interface name, link speed, or whether an interface is actually up. Here's every command you need.

TL;DR

ip link show              # all interfaces + state (UP/DOWN)
ip addr show              # interfaces + IP addresses
ip addr show eth0         # specific interface
ethtool eth0              # link speed, duplex, autoneg

ip link: Interface State

ip link show

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP
    link/ether 52:54:00:ab:cd:ef brd ff:ff:ff:ff:ff:ff
3: eth1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN
    link/ether 52:54:00:12:34:56 brd ff:ff:ff:ff:ff:ff

Key flags in <...>:

  • UP — interface is administratively up
  • LOWER_UP — physical link is connected (cable plugged in)
  • NO-CARRIER — cable is disconnected or link is down

state UP vs state DOWN:

  • UP — interface is enabled and has a link
  • DOWN — disabled or no physical link
  • UNKNOWN — loopback (always shows UNKNOWN, this is normal)

ip addr: IP Addresses

# All interfaces with IPs
ip addr show

# Specific interface
ip addr show eth0

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP
    link/ether 52:54:00:ab:cd:ef brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.100/24 brd 192.168.1.255 scope global dynamic eth0
       valid_lft 84721sec preferred_lft 84721sec
    inet6 fe80::5054:ff:feab:cdef/64 scope link
       valid_lft forever preferred_lft forever
  • inet — IPv4 address and prefix
  • inet6 — IPv6 address
  • scope global — routable address
  • scope link — link-local only (not routable)
  • dynamic — assigned by DHCP
# Just the IP, no other info
ip addr show eth0 | grep "inet " | awk '{print $2}'
# 192.168.1.100/24

ifconfig: Legacy Alternative

# Install if needed
apt install net-tools

ifconfig                  # all interfaces
ifconfig eth0             # specific interface

ip is the modern replacement. Use it instead — ifconfig is deprecated.

ethtool: Physical Link Details

ethtool eth0

Settings for eth0:
    Supported link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Full
    Advertised link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Full
    Speed: 1000Mb/s
    Duplex: Full
    Auto-negotiation: on
    Link detected: yes

Key fields:

  • Speed — current link speed
  • Duplex — Full (normal) or Half (old/problem)
  • Auto-negotiation — should be on for most NICs
  • Link detected: yes/no — physical cable connected?
# Check statistics (errors, drops)
ethtool -S eth0 | grep -E "rx_errors|tx_errors|rx_dropped|tx_dropped"

Bring Interface Up or Down

# Bring interface up
ip link set eth0 up

# Bring interface down
ip link set eth0 down

# Bounce interface (down + up)
ip link set eth0 down && ip link set eth0 up

Note: On systems managed by NetworkManager, use nmcli instead to avoid config conflicts:

nmcli device connect eth0
nmcli device disconnect eth0

Real Examples

Find all interfaces and their IPs

ip -br addr show

lo      UNKNOWN  127.0.0.1/8 ::1/128
eth0    UP       192.168.1.100/24 fe80::1/64
eth1    DOWN

-br (brief) gives a compact, readable summary.

Find the default network interface

ip route | grep default
# default via 192.168.1.1 dev eth0 proto dhcp

# Interface for outbound traffic
ip route get 8.8.8.8 | grep dev
# ... dev eth0 ...

Check for interface errors

ip -s link show eth0

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500
    link/ether 52:54:00:ab:cd:ef
    RX:  bytes  packets  errors  dropped  missed  mcast
    1234567890  9876543       0        0       0      0
    TX:  bytes  packets  errors  dropped  carrier collsns
     987654321  8765432       0        0       0       0

Non-zero errors or dropped = interface-level problems (bad cable, speed mismatch, NIC issues).

Find interface by IP

ip addr show | grep "192.168.1.100"
# inet 192.168.1.100/24 brd 192.168.1.255 scope global eth0

Check MTU

ip link show eth0 | grep mtu
# mtu 1500

# Change MTU
ip link set eth0 mtu 9000   # jumbo frames

Network Interface Naming

Modern Linux uses predictable names instead of eth0:

Name pattern Meaning
eth0 Old kernel naming (still used in VMs)
ens3, ens33 PCI slot naming (most cloud VMs)
enp1s0 PCI bus naming
eno1 Embedded NIC (on-board)
wlan0, wlp3s0 Wireless interfaces
lo Loopback 
# List all interface names quickly
ls /sys/class/net/
# or
ip link show | grep "^[0-9]" | awk '{print $2}' | tr -d ':'

Common Mistakes

Mistake 1: Interface shows UP but no link state UP means administratively enabled. LOWER_UP means physical link is connected. An interface can be UP without LOWER_UP (cable disconnected):

ip link show eth0
# <BROADCAST,MULTICAST,UP,NO-CARRIER>   ← admin up, but no cable
# <BROADCAST,MULTICAST,UP,LOWER_UP>     ← up with working link

Mistake 2: Using ifconfig on interfaces that ip doesn't show If ip addr show shows an interface but ifconfig doesn't, you have old net-tools. ip is correct.

Mistake 3: Not checking errors with -s High packet errors or drops indicate hardware or cable problems, not software issues.

Quick Reference

ip link show              # all interfaces + state
ip -br addr show          # brief: name + state + IPs
ip addr show eth0         # specific interface
ip -s link show eth0      # with statistics
ethtool eth0              # speed, duplex, link detected
ip route show             # routing table
ip link set eth0 up/down  # enable/disable

# Legacy (ifconfig)
ifconfig                  # all interfaces
ifconfig eth0             # specific interface

Conclusion

ip link show for interface state. ip addr show for IP addresses. ip -br addr show for a clean one-liner overview. ethtool eth0 when you suspect a physical link problem. For interface errors (dropped packets, RX errors), add -s to ip link. ip completely replaces ifconfig — use it.

Related: Restart Network Service Linux — apply interface configuration changes. Cannot Connect to Server Linux — interface check is step 1 in connectivity debugging.

Tags

#linux#networking#troubleshooting#infrastructure
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