arp -a shows (incomplete) Networking Origin: Network OSI layer 2 · Data Link Last updated 5 Nov 2026

Networking: `arp -n` shows (incomplete) / Destination Host Unreachable — no ARP reply from the next hop

The machine asked "who has this IP?" and nobody on the local network answered.

Exact message you may see arp -a (incomplete)192.168.1.20 dev eth0 FAILED192.168.1.20 dev eth0 INCOMPLETEARP request unansweredat <incomplete> on eth0
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Seen on: Linux Windows Networking

Meaning

ARP failing on the same subnet means the target is off, on another VLAN, has a different IP, or a switch/Wi-Fi isolation feature blocks the broadcast. Verify the IP and subnet mask, check the VLAN and port, and capture with tcpdump -i eth0 arp.

Common causes

  • Target host is down or unplugged
  • Wrong IP or subnet mask
  • Different VLAN or Wi-Fi client isolation
  • Switch dynamic ARP inspection blocking
  • Firewall on the target dropping ARP/ICMP

⚡ Quick fix

  1. Confirm both hosts share subnet and VLAN
  2. Watch the request: sudo tcpdump -ni eth0 arp
  3. Disable client isolation or fix the VLAN

Detailed fix by platform

Linux

  1. ip neigh show | grep -E "FAILED|INCOMPLETE"; sudo arping -I eth0 192.168.1.20

How to diagnose

  1. Neighbour state — FAILED/INCOMPLETE?
  2. Subnet/VLAN — Same?
  3. Target — Powered on?

🔧 Still not fixed?

Many errors look alike. If the steps above didn’t solve it, one of these is probably what you’re facing:

Where this error sits

Origin: Network. Errors that are often confused with or caused by this one (click to open):

4-way handshake timeout / Incorrect password — Networking: wlan0: WPA: 4-way handshake failed - pre-shared key may be incorrect / WRONG_KEY (Networking)4-way handshake timeo…Cannot assign requested address (EADDRNOTAVAIL) — Networking: connect: Cannot assign requested address — ephemeral port range exhausted by TIME_WAIT connections (Networking)Cannot assign request…DHCPDISCOVER: no free leases — Networking: dhcpd: DHCPDISCOVER from aa:bb:cc:dd:ee:ff via eth0: network 192.168.1.0/24: no free leases (Networking)DHCPDISCOVER: no free…Duplex mismatch: late collisions / CRC errors — Networking: Duplex mismatch — late collisions, runts and CRC errors on the switch port (Networking)Duplex mismatch: late…MAC flapping / broadcast storm (spanning tree loop) — Networking: %SW_MATM-4-MACFLAP_NOTIF: Host is flapping between ports / broadcast storm (Networking)MAC flapping / broadc…Many sockets in CLOSE_WAIT — Networking: Thousands of sockets in CLOSE_WAIT — the application is not closing its side of the connection (Networking)Many sockets in CLOSE…Native VLAN mismatch / wrong VLAN, no connectivity — Networking: %CDP-4-NATIVE_VLAN_MISMATCH / device on the wrong VLAN can't reach the gateway (Networking)Native VLAN mismatch …Network cable unplugged / NO-CARRIER — Networking: Network cable unplugged / `ip link` shows NO-CARRIER state DOWN / Ethernet: Network cable unplugged (Networking)Network cable unplugg…arp -a sh…

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