Hello @FredGermain,

Because the router is the DHCP Server, if you don't power it on, it won't work and assign the IP address to your switch's clients.

Or did you have another DHCP Server in your network?

  @FredGermain 

The DHCP server will not assign an IP address if it is not asked to do so. The DHCP server does not advertise its services, either. There is no provision for that in the DHCP protocol. A DHCP client needs to send a request for an IP address itself. If there is no DHCP server on the network, requests for DHCP addresses remain unanswered. Therefore, the client devices either use their default IP addresses or so-called link-local IP addresses. Some devices periodically resend their DHCP requests so they can obtain IP addresses once the DHCP server is available, but some don’t. Google “DHCP DORA” for details on DHCP.