[USG Flex H - V1.39(ABZH.0)ITS-260800686] - User Custom DDNS effective IP not appear

Maverick87

Yes but for Dynu there isn't any effective IP listed. So I think it's a visual bug.

PeterUK

I think your missing the obvious the way you have done Dynu is by custom which has auto but the pre set No-IP has no auto

Maverick87

And this is clear… but…

1: Why for the custom entry there isn't "Interface" as IP Address

2: What changes between the two types for the effective IP? The only thing can be that the effective IP is "calculated" throught a "return" call from the service and for the custom service, is unknown (also if can be implemented a field for return, so can be called after the update, if the service have it)

PeterUK

Well I don't know why there is no Interface option for custom.

The way DDNS works for auto is it never knows what IP to send to the DDNS server it just say hello can you see what IP I'm from and use that thanks and if the interface IP changes DDNS is triggered again. Thats all I know about auto.

If you want to see effective IP you can use Public IP option which I think I had a hand in Zyxel doing.

Maverick87

Hi Peter,

After change the WAN IP, now seems that the effective IP is showed into the table without touch the configuration, just renewed the WAN IP.

But…

Seems there is a failure on User custom when I click on "Update" button… for the No-Ip, after the update, the IP under "Effective IP" return valid, instead for the "User custom" not (it's blank).

@Zyxel_Melen , @Zyxel_Judy, @Zyxel_Luna can you check this problem?

Thank you

PeterUK

So I relooked at this as dynu still supports http for DDNS so you can see whats happening

GET /nic/update?hostname=Zyxel-DDNS-test.freeddns.org HTTP/1.0

Authorization: Basic =

User-Agent: ZyWALL/1.0

Host: apiserver.dynu.com
HTTP/1.1 200 OK

Date: Sun, 16 Aug 2026 13:6:38 GMT

Server: Dynu Web Server

X-Powered-By: Dynu Dynamic DNS Service

Content-Length: 17

Content-Type: text/html; charset=UTF-8

Connection: close
good 92.239.74.95

So there is return of what IP dynu sees and effective IP shows but then if you update again see

GET /nic/update?hostname=Zyxel-DDNS-test.freeddns.org HTTP/1.0

Authorization: Basic =

User-Agent: ZyWALL/1.0

Host: apiserver.dynu.com
HTTP/1.1 200 OK

Date: Sun, 16 Aug 2026 13:9:46 GMT

Server: Dynu Web Server

X-Powered-By: Dynu Dynamic DNS Service

Content-Length: 5

Content-Type: text/html; charset=UTF-8

Connection: close
nochg

which causes Flex to show no effective IP

Maverick87

Hi Peter,

so you tell me that Dynu don't update the IP if the current IP is the same that have already? And in this context the IP return is empty because Dynu not have updated the IP?

Probably can be this the problem…

PeterUK

yes looks that way if Dynu sends back nochg this means your IP is the same it saw last time by Dynu but then because nochg is not a IP this looks to make the effective IP not show anything.

Zyxel_Luna

Hi @Maverick87 @PeterUK @kelmi ,

Thank you for your discussion and analysis.

Because Dynu DDNS has its own specific DNS update mechanism, it is not fully compatible with our [User Custom] mode. In the upcoming firmware release, we will update and fix the issues related to the [Dynu Basic] mode. By then, you will be able to switch to [Dynu Basic] for better compatibility.

Thank you very much for your patience and continued support.

Maverick87

Hi @Zyxel_Luna,

Thank you for your help.

Two things:

• Also when the IP is real refreshed, the field still remaining empty;
• Can you share the beta firmware when the issue is fixed?

Thank you