It's just !
I had forgotten this subtlety that the gateway is number 0.
In MQTT what interests me is the topic of publication and subscription of the gateway.
Thank you.

Thank you for your reply.
I understand the objective but there is one point that does not seem to me to be appropriate: in my case, the indicated payload is 0 but the node number that emits is 205.
mhs4-out0/205/255/3/0/21 - payload : 0

Hello,
I have an MQTT ethernet gateway and a relay type node. Both are powered on mains.
The relay type node is registered in the controller and it is working properly.
But sometimes the relay type node sends an internal message type I_DISCOVER_RESPONSE with a payload of 0.
I do not see what this message is for and if the controller has to answer.
Can you explain to me ?
Thank you.

The 2.2.0-rc.1 version in development seems to solve the problem.
See also the message : https://forum.mysensors.org/topic/6684/serial-gateway-restarting/30
Can you explain the change in the new version?
Thank you.

Arduino/Genuino Uno

Arduino AVR Boards Built-In by Arduino version 1.6.18

Board def :

BN: Carte inconnue
VID: 1A86
PID: 7523
SN: Envoyez un croquis pour l'obtenir

Maybe that's the explanation ...
My gateway is mains powered with 9V and 500mA power.

Nobody found this problem?

It is true that a node relay type should normally be always powered if you want to control ...

I will see if I can test with a more powerful diet.
Thank you.

Arduino IDE : 1.8.2
API MySensors : 2. 1. 1

I rephrase my question:

When the remote node is powered on, the gateway receives the MQTT message and transmits it to the node. It's OK.

When the remote node is not powered on, the gateway receives the message MQTT but reboots immediately.
It would seem that the remote node not powered up disturbs the gateway.

Thank you.

Arduino UNO R3 + Ethernet shield W5100 + NRF24L01+

Thank you.