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3
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{bug Report] ULA IPs in the fd00::/8 subnet range rejected when setting as a manual DNS server IP

 
3
Votes

{bug Report] ULA IPs in the fd00::/8 subnet range rejected when setting as a manual DNS server IP

{bug Report] ULA IPs in the fd00::/8 subnet range rejected when setting as a manual DNS server IP
{bug Report] ULA IPs in the fd00::/8 subnet range rejected when setting as a manual DNS server IP
2025-09-28 03:29:40
Tags: #IPv6
Model: Deco BE65 Pro  
Hardware Version: V1
Firmware Version: 1.2.0

As reported back in 2023 (https://community.tp-link.com/en/home/forum/topic/604494) the app doesn't allow IPv6 DNS server IPs in the ULA (fd00::/8) range to be used, saying the IP is invalid.

 

This isn't correct, they are just as valid as RFC1918 IP ranges, such as 192.168.0.0/16, they just aren't globally routable, the same as RFC1918 addresses aren't.

 

This would solve the problem of when, not if, you change ISPs or if your current ISP changes the subnet allocated to your connection for whatever reason.

 

For more info, I posted details to this thread along with other weird IPv6 issues and quirks I've come across since upgrading to my Deco BE65 Pro routers:

 

https://community.tp-link.com/en/home/forum/topic/838180

#1
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3 Reply
Re:{bug Report] ULA IPs in the fd00::/8 subnet range rejected when setting as a manual DNS server IP
2025-09-29 06:48:52

  @evilbunny 

Hi, thank you very much for the feedback.

It might not be a bug. Deco IPV4 settings also require the customized IPV4 Primary/Secondary DNS servers to be a public IPV4 address. A similar approach may be applied to IPV6 DNS settings. After checking with the senior engineer, it is planned to extend this allowance to include customized DNS IPs within the fd00::/8 subnet range.

Thanks a lot.

Best regards.

 

 

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#2
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Re:{bug Report] ULA IPs in the fd00::/8 subnet range rejected when setting as a manual DNS server IP
2025-09-29 06:53:45

You are correct that only routable addresses are accepted for DNS server IPs for the router itself, but the DHCPv4 section does accept RFC1918 addresses which are then sent to clients in DHCPv4 replies.

 

It's good news to hear that there is plans to extend the IP validation to accept ULA addresses.

#3
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Re:{bug Report] ULA IPs in the fd00::/8 subnet range rejected when setting as a manual DNS server IP
2025-10-11 06:20:21

Dear TP-Link,

 

Please allow for my Deco BE85 to set IPv6 DNS Address to be
Link-Local Address (LLA, FE80::/64) or/and Unique Local Address (ULA, FD00::/8).

 

Right now Deco iOS application only allow to set IPv6 DNS Address as any Global Unicast Address (GUA, 2000::/3),
but Deco iOS application does NOT allow to set IPv6 DNS Address to be Link-Local Address (LLA, FE80::/64) or/and Unique Local Address (ULA, FD00::/8).

 

I'm running my own DNS server inside local network (Pi-hole),
which working perfectly fine for IPv4 (DNS address set at IPv4 DHCP settings as 192.169.1X, outside of auto assigned range), 
but I forced to disable IPv6 because I can NOT set IPv6 DNS Address for my local DNS server.

 

Best Regards,
Vlad
 

#4
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