networking layer2 ai_generated true

NDP: Duplicate address detected for fe80::1 on eth0, DAD failed

ID: networking/ndp-duplicate-address

Also available as: JSON · Markdown · 中文
81%Fix Rate
87%Confidence
1Evidence
2024-09-12First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
Linux kernel 6.1.0-17-amd64 active — — —
Windows Server 2022 IPv6 stack active — — —
Cisco IOS 15.9(3)M active — — —
FreeBSD 14.0 active — — —

Root Cause

Duplicate Address Detection (DAD) for an IPv6 link-local address failed because another host on the same link is already using that address, typically due to manual configuration overlap or a rogue device.

generic

中文

IPv6链路本地地址的重复地址检测（DAD）失败，因为同一链路上的另一台主机已在使用该地址，通常是由于手动配置重叠或恶意设备。

Official Documentation

https://datatracker.ietf.org/doc/html/rfc4862

Workarounds

  1. 90% success Manually assign a unique link-local address on the local host: `ip addr add fe80::2/64 dev eth0` and remove the conflicting one 
    Manually assign a unique link-local address on the local host: `ip addr add fe80::2/64 dev eth0` and remove the conflicting one
  2. 85% success Identify the conflicting host by scanning the neighbor cache: `ip -6 neigh show dev eth0`, then disconnect or reconfigure it 
    Identify the conflicting host by scanning the neighbor cache: `ip -6 neigh show dev eth0`, then disconnect or reconfigure it

中文步骤

  1. Manually assign a unique link-local address on the local host: `ip addr add fe80::2/64 dev eth0` and remove the conflicting one
  2. Identify the conflicting host by scanning the neighbor cache: `ip -6 neigh show dev eth0`, then disconnect or reconfigure it

Dead Ends

Common approaches that don't work:

  1. 90% fail

    This allows duplicate addresses to persist, causing packet loss and connectivity issues for both hosts.

  2. 70% fail

    The duplicate address is still used by the other host; the local host may get a new address but the conflict is not resolved.

  3. 80% fail

    The duplicate address on the remote host remains; the local host will generate the same address again based on its MAC, leading to the same DAD failure.