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IPv6 duplicate address and dadfailed

Written by: on 29 January 2020 03:54 PM 29 January 2020 03:54 PM

Solving the issue with IPv6 when DAD is failed

Symptoms:

  1. A lot of entries in the system log looking like this:

    kernel: [xxxx.yyyy] eth0: IPv6 duplicate address aaaa:bbbb:cccc:d:eee:fff:aaaa:aaaa detected!


    Where last several numbers in IPv6 address are matching the network interface MAC address.

  2. Public ETH interface shows "dadfailed" when you run "ip a":

    inet6 fe80::aaaa:bbbb:cccc:dddd/64 scope link dadfailed

 

Fix:

Edit the file /etc/sysctl.conf and insert following lines into it:

net.ipv6.conf.eth0.accept_dad = 0
net.ipv6.conf.default.accept_dad = 0
net.ipv6.conf.eth0.dad_transmits = 0
net.ipv6.conf.default.dad_transmits = 0

Where "eth0" is your Ethernet interface name.

Then run: 

sysctl -p

And restart networking:

service network restart

OR

service networking restart

Or just reboot the VPS.

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