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

**Code:** `arp -a shows (incomplete)` · **Category:** Networking · **Seen on:** Linux, Windows, Networking

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

## 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?

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Source: [WhatIsMyError](https://whatismyerror.com/errors/networking/arp-incomplete-no-reply)