I don't have access to the Deco because it is in a different location. I do know the MAC address of the Wireless interface:

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b0:a7:b9:ae:38:78

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Is that the same MAC address that is printed on the bottom of the router?

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If so, is the WAN MAC address b0:a7:b9:ae:38:79?

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I cannot clone the MAC address because I have to be logged in to the local LAN to do this. Right now I only have cloud access to the router which doesn't allow MAC cloning.

  @Ratsima 

If you have access to Deco app, what MAC address it shows under Main Deco page should be its WAN MAC address. Just checked that with my Deco mesh and ISP Router.

Also, it is the same MAC address that is printed on the label on the bottom of Main Deco, at least in my case.

The only MAC address shown in the app is B0-A7-B9-AE-38-78.

The web based info-only page shows:

LAN

MAC Address: B0-A7-B9-AE-38-78

But, isn't that the Wireless interface MAC address?

Since I don't have the Deco here, I can't know what's printed on the label.

  @Ratsima 

Give that to your condo management. See if it works.

I have Main Deco connected to ISP Router. In Deco app, in Web interface and on the label on the bottom of Main Deco I see one and same MAC address. That same MAC address is reported for Main Deco in ISP Router - and I use that MAC address to allocate static IP address in ISP Router for my Main Deco.

The wireless interface MAC address for my Main Deco is different and I can only find it with WiFi Analyzer. There are two different MAC addresses, actually, one for 5GHz and another for 2.4GHz, and they are not the same as the one from above. 

  @Alexandre. 

Thank you.

I had given that MAC address to the condo management yesterday. Overnight they completed their migration to a MicroTik router running RouterOS. I'm logged in without having to use a password, so I assume that the MAC address works for automatice log in.

  @David-TP  I gave the condo IT staff:  b0:a7:b9:ae:38:78

However, I also told them that they could get the actual WAN MAC address from their own router.

So, I don't really know if they used  b0:a7:b9:ae:38:78 or if they otherwise obtain the WAN address.

It has been my understanding that each interface ordinarily has its own MAC address. One for the WAN interface, one for the Wireless interface and one each for the wired interfaces.

For example, my Mac has dual homing:

Wireless: en0: 98:10:e8:f1:c7:65

Wired:    en1: 98:9e:63:39:8b:ec

  @David-TP 

I have Deco M9 Plus and I run my Deco mesh in Access Point mode.

On the bottom of my Main Deco M9 Plus there is label with the MAC address printed on it. I see same MAC address in Deco app for Main Deco, and in ISP Router to which Main Deco is connected. I see same MAC address in Web interface for Main Deco.

I also use that MAC address to assign to it static IP address in my ISP Router. I can confirm that my Main Deco reports IP address which is same as one assigned to that MAC address in ISP Router.

I am assuming from what I see that this MAC address is not, actually, LAN MAC address.

Original post was asking for MAC address of Main Deco, to be whitelisted by condo management. From what I can see, MAC address on the Deco label, which is the same as in Deco app and in web interface for Main Deco, would be the right IP address to provide to condo management. This is MAC address that Main Deco provides to usptream networking gear it is connected to.

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Unless, of course, if I switch Deco to Router mode, it'll provide different MAC address to ISP Router than what is printed on the label, but I won't be testing that, because I need my WiFi network up and running all day. 

  @Alexandre. 

See this Wikipedia article: MAC Address which contains this:

Network nodes with multiple network interfaces, such as routers and multilayer switches, must have a unique MAC address for each NIC in the same network. However, two NICs connected to two different networks can share the same MAC address.

In other words, the Deco X20 should have three MAC addresses: one for the Wireless interface, one for the Wired LAN (Ethernet) interface and one for the WAN interface.