I have a new RT-AX88U Router. I am able to set the address of the router and define the range of IPs within my subnet assigned by the internal DNS to the main network. I have limited the range to 2-99 so I can have fixed IP addresses in the range above 99. However, I also have a guest network enabled for both 2.4GHz and 5GHz. On those networks, the router seems to assign IPs on a different subnet, and I cannot find any information on how those IPs are determined or any way to control their assignment. For example, if the main router is 192.168.1.1, then all my IPs on the main network are in the range 192.168.1.*. However, on the guest networks, the gateway shows as 192.168.101.1, and it assigns IPs within 192.168.101.*, but sometimes within 192.168.102.*. The ones with 192.168.102.* may be on the 5GHz network. This seems to be a default feature that cannot be changed. For the most part, this works OK. However, I have a few devices that don't reconnect well with DNS, and I want to use fixed IPs. I see no way to avoid future conflicts with the DNS on these guest networks. What I have done is note the IPs assigned by the DNS to some devices, and set a fixed IP on the same subnet but with a specific last number not already used. I use the guest networks mostly for smart home devices that I keep isolated from the main network (internet only) for security purposes.

Does anyone know how the DNS works on guest networks, and whether there is any way to control it? I have not found any information in any manuals or help pages.