[BUG] Unit Name not used for DHCP registration and worse uses hostname with illegal underscore

[bsiege]

Unit Name set to "naehtisch"

ISC DHCPD wants to register. BIND log:
zone int.some.org/IN/internal (unsigned): ESP_9C56D1.int.some.org/A: bad owner name (check-names)

Expected behavior
instead of ESP_9C56D1 there should be naehtisch

Screenshots
If applicable, add screenshots to help explain your problem.

Used platform (please complete the following information):
Build: ESP_Easy_mega_20260121_collection_A_ESP8266_4M1M Jan 21 2026

[TD-er]

Hmm that ESP_xxx should not happen.
I will have a look at it, as this is typically a problem where the hostname is set at the wrong time.

[TD-er]

Could you also try one of this build?
It has the network code completely rewritten
https://td-er.nl/ESPEasy/latest/

Make sure you flash it via the serial port, or at least have the node connectable to a computer as there is still an issue with OTA update on ESP8266 to this build.

I then know whether it is fixed at least in the upcoming build.

[bsiege]

tested Build: ESP_Easy_mega_20260220_collection_A_ESP8266_4M1M Feb 20 2026

Behavior not changed. Forced other "Unit names" and rebooted. DHCP server still gets the faulty name:

22-Feb-2026 23:38:29.834 general: zone int.some.org/IN/internal (unsigned): ESP_9C56D1.int.some.org/A: bad owner name (check-names)
22-Feb-2026 23:38:29.849 general: zone int.some.org/IN/internal (unsigned): ESP_9C56D1.int.some.org/A: bad owner name (check-names)
22-Feb-2026 23:40:07.380 general: zone int.some.org/IN/internal (unsigned): ESP_9C56D1.int.some.org/A: bad owner name (check-names)

btw: wifi client name changes as expected, it must be the DHCP client part...

[TD-er]

Well the "ESP_xxxx" name used for the DHCPc should not be happening. So I must have changed something where the hostname isn't set (or cleared) before the ESP tries to (re)connect.

Can you show what flags are being set on the WiFi Station network interface tab?
For example is "Enable SDK WiFi Auto Reconnect:" checked? If so, can you test with this disabled?

Do you use static IP? Hidden SSID? What WiFi channel is used (this makes a difference when using a channel > ch.11 and hidden SSID)

[bsiege]

no static IP (but reserved IP in DHCP Server)
no hidden SSID
connected @ ch.1
"Periodical send Gratuitous ARP" is set.
"Hidden SSID Slow Connect:" is set.

One Rule:
on System#Wake do
vol,25
endon

[TD-er]

OK, so nothing special.
And just to be sure, it is with ESP8266 as you linked in the start post, right?

[bsiege]

yes, Olimex-EVB

[TD-er]

Can you check with the code from this GH Actions build to see if it has been fixed?
https://github.com/letscontrolit/ESPEasy/actions/runs/22319275946

Or pick one of 2 builds I uploaded here: https://www.dropbox.com/scl/fi/vb39k58f0j3dgzzgz96mc/ESP_Easy_mega_20260223_normal_ESP8266_4M1M.zip?rlkey=f3b304piwre5s3okz3lo595i2&dl=0 (has both 'normal' and 'Collection A' for ESP8266 in the zip file)

[bsiege]

Build: ESP_Easy_mega_20260223_normal_ESP8266_4M1M Feb 23 2026
Nope, the DHCP selector seems to be written in stone. ESP_9C56D1 correlates to ESP Chip ID: 0x9C56D1
Renamed device and restarted twice, never takes the Unit Name as hostname

[bsiege]

Ouch:

I am very, very sorry! After another debug round i found the issue which was fully my fault:
Saw that the registration packet had correct name in packet. It must been more than 3 years ago, that i made a reservation for this device in DHCP and accepted the initial, then not RFC conform name. And this overrules the sent hostname.

Again, i am very sorry to waste your time!

[TD-er]

Again, i am very sorry to waste your time!

Well just to reassure you didn't, as I've also seen it happen here on my node :)
On the Network tab you can see the actual hostname of the network interface as I do query the interface and not place there what I may have intended to be the hostname.

On the ESP8266 there simply was no call to set the hostname on the first call.

So you may have set the DHCP server to use that specific IP, but that entry is linking a MAC address to an IP-address.
What your DHCP server/router shows is likely the last requested hostname and then caches that hostname for the TTL duration of that DHCP lease.

Just to be sure, you could flash an older build and see the hostname as reported on the Network tab in ESPEasy will show an ESP_xxxxxx hostname. Maybe if the hostname isn't set, the echo'ed hostname in the DHCP reply is then internally set as hostname, that's possible.

TL;DR
It was a true bug on ESP8266-build of ESPEasy/

[TD-er]

Oh there seems to be another bug still present.
If the ESP just reconnects to the AP, the hostname can still be this "ESP_xxxxxx" which is then suddenly changed to the intended hostname a number of seconds later.
So it is possible the DHCP-client call may still have this wrong hostname when it reconnects.

[TD-er]

Hmm not sure what causes this, as I now really set the hostname before calling WiFi.begin

It may have something to do with the autoreconnect....