# DHCP DECLINE: address 192.168.1.100 already in use on the network

- **ID:** `networking/dhcp-address-already-used`
- **Domain:** networking
- **Category:** network_error
- **Verification:** ai_generated
- **Fix Rate:** 88%

## Root Cause

A DHCP client detected via ARP probe that the offered IP address is already in use by another host, so it sent a DHCPDECLINE to the server.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| ISC DHCP 4.4.3 | active | — | — |
| dnsmasq 2.89 | active | — | — |
| systemd-networkd 250 | active | — | — |

## Workarounds

1. **Identify and remove the conflicting static IP host, then release the address: arp -d 192.168.1.100; dhclient -r eth0; dhclient eth0** (90% success)
   ```
   Identify and remove the conflicting static IP host, then release the address: arp -d 192.168.1.100; dhclient -r eth0; dhclient eth0
   ```
2. **Exclude the conflicting address from the DHCP pool in the server config (e.g., in dhcpd.conf: deny 192.168.1.100;)** (85% success)
   ```
   Exclude the conflicting address from the DHCP pool in the server config (e.g., in dhcpd.conf: deny 192.168.1.100;)
   ```

## Dead Ends

- **** — The conflict is due to a static IP assignment on another host; restarting the server does not resolve the conflicting address. (90% fail)
- **** — Lease time does not affect address conflicts; the client's ARP probe detects the conflict regardless of lease duration. (95% fail)