Dynamic DNS doesn't notice that IPv6 prefix has changed



  • I have a 2 ipv6 dynamic dns (cloudflare) addresses set up. One pointing to the WAN interface and one pointing to the LAN i/f.

    Normally my ISP always provides the same /56 prefix to my router. Sometimes, rarely, if I am rebooting I will get a different prefix temporarily, but then it will figure it out and get my old prefix back.

    When this happens I see that the DDNS update happens on cloudflare when the temporary prefix takes affect. However, when the original /56 prefix becomes active the DDND on the LAN i/f does not update cloudflare. My guess is that the WAN ipv6 address stays the same, but the prefix changes and the dynamic dns service doesn't know that the change occurred.

    The funny thing is, the status that shows the ipv6 address in the DDNS is red, which makes me think it knows something is wrong.

    The only way i can get the DDNS to update is to do a force update.



  • @IsaacFL said in Dynamic DNS doesn't notice that IPv6 prefix has changed:

    Normally my ISP always provides the same /56 prefix to my router. Sometimes, rarely, if I am rebooting I will get a different prefix temporarily, but then it will figure it out and get my old prefix back.

    Do have "Do not allow PD/Address release" on the WAN page selected?



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  • @JKnott It is selected.

    The actual change doesn't bother me, now that I expect that it might happen. It happens very rarely, and only when I have rebooted a couple of times. I just do the save WAN I/f and it goes back to my original prefix. Even if I do nothing it will change back on it's own, usually less than 30 minutes.

    The issue, is that the DDNS doesn't catch the fact that the prefix changed back. It sees the transient prefix and updates cloudflare, but when the prefix gets corrected, the DDNS doesn't update cloudflare again.

    My guess is that the WAN ipv6 address stays the same during this process, and DDNS update only fires when WAN address changes.



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  • @IsaacFL Black cats always are. I used to have one, Mush (rhymes with 'push'). She always got the last word. Always.



  • @IsaacFL said in Dynamic DNS doesn't notice that IPv6 prefix has changed:

    The issue, is that the DDNS doesn't catch the fact that the prefix changed back. It sees the transient prefix and updates cloudflare, but when the prefix gets corrected, the DDNS doesn't update cloudflare again.

    Given that you have the same prefix, except briefly after rebooting, why are you using a dynamic DNS? Just use a normal DNS where you map names to addresses. That would simply mean that the host name won't work for that brief time.

    I have a public DNS that's not dynamic and it just works.



  • @JKnott that is exactly what I do for all of my other hosts. Manual entries in the DNS.

    The plan was to have the DDNS set to notify me by email if the prefix ever changes but I noticed never got an email when it actually occurred.

    I am also using this in conjunction with uptime robot.

    I can adjust it to use the WAN instead for this but it seems this is a bug since it is possible for the WAN ip to stay the same but have the prefix change.


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