networking network_error ai_generated true

DHCP: IP address 192.168.1.50 conflict detected with MAC 00:11:22:33:44:55

ID: networking/dhcp-ip-conflict

Also available as: JSON · Markdown · 中文
82%Fix Rate
88%Confidence
1Evidence
2023-08-10First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
ISC DHCP 4.4.3-P1 active — — —
dnsmasq 2.89 active — — —
Windows Server 2022 DHCP active — — —
Linux dhcpcd 10.0.2 active — — —

Root Cause

A DHCP server has detected that an offered IP address is already in use by another host on the network, typically due to a static IP assignment overlapping with the DHCP pool or a rogue DHCP server.

generic

中文

DHCP服务器检测到提供的IP地址已被网络上的另一台主机使用，通常是由于静态IP分配与DHCP池重叠或存在恶意DHCP服务器。

Official Documentation

https://kb.isc.org/docs/aa-00798

Workarounds

  1. 95% success Exclude the conflicting IP from the DHCP pool and assign it as a static reservation: `dhcpd.conf: range 192.168.1.100 192.168.1.200; host static-host { hardware ethernet 00:11:22:33:44:55; fixed-address 192.168.1.50; }` 
    Exclude the conflicting IP from the DHCP pool and assign it as a static reservation: `dhcpd.conf: range 192.168.1.100 192.168.1.200; host static-host { hardware ethernet 00:11:22:33:44:55; fixed-address 192.168.1.50; }`
  2. 80% success Run `arp -d 192.168.1.50` on the DHCP server to clear the ARP cache, then force the client to renew: `dhclient -r && dhclient` 
    Run `arp -d 192.168.1.50` on the DHCP server to clear the ARP cache, then force the client to renew: `dhclient -r && dhclient`

中文步骤

  1. Exclude the conflicting IP from the DHCP pool and assign it as a static reservation: `dhcpd.conf: range 192.168.1.100 192.168.1.200; host static-host { hardware ethernet 00:11:22:33:44:55; fixed-address 192.168.1.50; }`
  2. Run `arp -d 192.168.1.50` on the DHCP server to clear the ARP cache, then force the client to renew: `dhclient -r && dhclient`

Dead Ends

Common approaches that don't work:

  1. 75% fail

    The conflicting IP is still in the pool and may be reassigned, causing the same conflict again unless the pool or static assignment is fixed.

  2. 65% fail

    Longer leases make conflicts persist longer and do not address the root cause of overlapping addresses.

  3. 90% fail

    This hides the problem but allows duplicate IPs to be assigned, leading to intermittent connectivity issues and ARP conflicts.