@jra11500 

Hi,

In the original Wi-Fi standards there is no provision for a client device of a wireless network to "redistribute" that network to further client devices.

Since there has always been user demand for ways to split one wireless connection to multiple client devices companies have created a few solutions. 

For one thing they developed other standards that they put on top of the original Wi-Fi standards. An early example is WDS (which, however, isn't a true standard) and more recently the various "Mesh" standards (like EasyMesh, OneMesh, Deco Mesh and many more) showed up.
But the one big disadvantage of all these standards is that for things to work both, the host network device and the client network device need to support the same standard.

So, another solution that came up are the "ordinary" wireless range extenders, which are often advertised as "Works with any Wi-Fi router".
These extenders don't require the device providing the host wireless network to support any additional standards.
To achieve what isn't supposed to work in the first place these wireless range extenders do some clever "trickery" with MAC addresses (real ones and virtual ones) and the IP addresses. One could also say they sort of "fool" the host network device.
This often results in weird things being noticeable in the clients list of the host router, with the particular behavior varying depending on the router model.

When you connect more client devices to the RE700X you might see even more IP addresses showing up for the same MAC address on your AX55 router.

  @woozle 

Thanks for the information.  Understanding basically how a device works allows one to dominate that device.  Seeing a virtual MAC and IP address made me wonder if the address reservation was set up and working correctly.  It turns out that it is working and there's nothing to worry about as long as I can access the extender's GUI.