Orbi Router (RBR50) configuration bug

> [...] I have enough devices to merit the 512-IP space.

   Perhaps, but you may not have enough router to handle that many.

> If I want to use the Router as a DHCP server, it does not respect my
> subnet, only allows me to provide a starting and ending IP with the
> final field blank.

   A design limitation, I'd guess, for a consumer-grade router.  I'd
expect trouble with more than just DHCP.  NAT, for example.  I'd also
worry about performance with more than 250 client devices.  (Safe bet it
wasn't tested that way.)

> Looks like the UI is hardcoded to only allow the 256-value range, not
> Subnet Mask-driven range.

   Did you also try a _more_ restrictive subnet mask?  It might be
"hardcoded" on one side, only.