Before establishing a Wifi Connection(computer Wifi Card to my Wifi modem) I list the available wifi access points, and have this Output:
~$ nmcli device wifi list


SSID MODE CHAN RATE SIGNAL BARS SECURITY
*wifi modem Infra 1 54Mbit/s 74 ▂▄▆_ WPA2


Then I start the Connection:
~$ nmcli c up wifi connection 1
Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/6

The Connection is activated, but if I retype ~$ nmcli dev wifi, to list the Wifi access Points near my location then I see that the modem access point is duplicated:
~$ nmcli device wifi list

SSID MODE CHAN RATE SIGNAL BARS SECURITY
*wifi modem Infra 1 54Mbit/s 69 ▂▄▆ WPA2
*wifi modem Infra 1 54Mbit/s 60 ▂▄▆ WPA2


I have only one Wifi Card on my computer(wlp3s0)
~$ nmcli device
DEVICE TYPE STATE CONNECTION
wlp3s0 wifi connected Wifi connection 1
enp7s0 ethernet unavailable --
lo loopback unmanaged --

My wifi router has maybe two Wifi Cards?

at least you see it, should be happy , people mostly report issue with wifi installation and not able to reach it from console

yes this could be situation and for detail inspection will need more details, like modem/router manufacturer and version, your wifi card manufacturer, linux version, nmcli version ...

output of
would be useful as well

however if you check internet you will find something similar described as a bug with different side effects.

From my personal experience cause could be that your router have same SSID for both bands,so 2.4GHz has the same weighting as 5GHz, but also if you experimenting with some wifi "hacking" tools that could produce such effect as aircrack-ng (forks), fern ...

you can also use this awk for limiting only one output per ssid

Any other devices in home or nearby that could mirror that signal like a dd-wrt router or wifi extender? I'd normally think two frequencies bands having same name.

@leemenix, thx for answer.

Nmcli version:
$ nmcli -v
nmcli tool, version 1.2.4

Linux version:
$ uname -mrs
Linux 4.8.0-22-generic i686

Computer connection devices:
$ nmcli device show

GENERAL.DEVICE: wlp3s0
GENERAL.TYPE: wifi
GENERAL.MTU: 1500
GENERAL.STATE: 100 (connected)
GENERAL.CONNECTION: Wifi connection 1
GENERAL.CON-PATH: /org/freedesktop/NetworkManager/ActiveConnection/12

GENERAL.DEVICE: enp7s0
GENERAL.TYPE: ethernet
GENERAL.MTU: 1500
GENERAL.STATE: 20 (unavailable)
GENERAL.CONNECTION: --
GENERAL.CON-PATH: --
WIRED-PROPERTIES.CARRIER: off

GENERAL.DEVICE: lo
GENERAL.TYPE: loopback
GENERAL.MTU: 65536
GENERAL.STATE: 10 (unmanaged)
GENERAL.CONNECTION: --
GENERAL.CON-PATH: --
IP4.ADDRESS[1]: 127.0.0.1/8
IP4.GATEWAY:
IP6.ADDRESS[1]: ::1/128
IP6.GATEWAY:

Maybe the router has a dual band, how can I check this on the wifi-router? I am not using aircrack-ng, neither other.
(I know my wifi computer card can be swiched to monitor, it is not operating in this mode, Mode:Managed, Frequency:2.467 GHz )

@jefro thx for answer,
I do not have any other devices at home.
My wifi-router has a wifi extender option but it is turned off, and it doesn't have a dd-wrt firmware.
Near my house there is a Linksys router, this firmware is commonly used in this routers.

But the duplicated access point output is a problem of Linux-Nmcli-Network Manager
because when I move elsewhere, far from my house and reset my router and my connection parameters the problem still remains.

The wifi router can be connected to 3g(UMTS) , 4g(LTE) or GSM.
The Wifi router protocol is 802.11 b/g/n
802.11 b operates in the 2.4 GHz band - interior scope 35 m, exterior scope 140 m.
802.11 g operates in the 2.4 GHz band - interior scope 38 m, exterior scope 140 m.
802.11 n operates on both 2.4 GHz and 5 GHz bands - interior scope 70 m (2,4 GHz)
12-35 m (5 GHz), exterior scope (2,4 GHz, 5 GHz) 250 m.

hi @lander9, seams like a bug, you should be proud

try on my Slackware, same situation here. will dig more after vacation, or maybe during vacation (please don't let my wife know)

but for your further investigation here is some close related findings, so far:

https://bugzilla.redhat.com/show_bug.cgi?id=1393997
https://bugzilla.redhat.com/attachme...03&action=edit
https://cgit.freedesktop.org/Network...9f1755b8ddfa30
https://gitlab.freedesktop.org/Netwo...NetworkManager

hello@leemenix,
I have no problem with my two wives: one for the night, another for the day.
Have a good vacation.