networking network_error ai_generated true

DHCP DECLINE: address 192.168.1.100 already in use on the network

ID: networking/dhcp-address-already-used

Also available as: JSON · Markdown · 中文
88%Fix Rate
88%Confidence
1Evidence
2023-11-20First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
ISC DHCP 4.4.3 active — — —
dnsmasq 2.89 active — — —
systemd-networkd 250 active — — —

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.

generic

中文

DHCP客户端通过ARP探测发现提供的IP地址已被其他主机使用，因此向服务器发送了DHCPDECLINE。

Official Documentation

https://datatracker.ietf.org/doc/html/rfc2131

Workarounds

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

中文步骤

  1. 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;)

Dead Ends

Common approaches that don't work:

  1. 90% fail

    The conflict is due to a static IP assignment on another host; restarting the server does not resolve the conflicting address.

  2. 95% fail

    Lease time does not affect address conflicts; the client's ARP probe detects the conflict regardless of lease duration.