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I have been having trouble with my wireless network card, both on Windows and Ubuntu, but in the case of Ubuntu my problem boils down to this: the laptop connects to the Wi-Fi just fine, authenticating properly and everything, but then doesn't connect to the internet and doesn't even have ping.

After a few hours of working with tech support, we managed to figure out that for some reason the network card doesn't send anything on 5GHz frequencies. It can receive frames and claims to send them, but a packet sniffer never sees them. Oddly enough, it seems that 2.4GHz networks work just fine. Most of the access points at my university and my dorm are hybrid, but they enforce a 5GHz preference to fit as many people as possible in.

I'm going to send my computer in for repairs soon, but until then I need a quick fix. I want to, if possible, deactivate the 5GHz capabilities of my network card so that it only broadcasts configuration for 2.4GHz and defaults to it so that I am connected to networks I can actually use. I don't mind losing the ability to connect to 5GHz-only networks, and I'm probably going to overhaul my entire setup, but until then, my question is this:

How do I disable my wireless card's 5GHz capabilities so that it only connects through 2.4GHz frequencies?

Some (hopefully useful) command dumps: 

ash@earia:~$ sudo lshw -class network
*-network               
   description: Wireless interface
   product: RTL8821AE 802.11ac PCIe Wireless Network Adapter
   vendor: Realtek Semiconductor Co., Ltd.
   physical id: 0
   bus info: pci@0000:02:00.0
   logical name: wlp2s0
   version: 00
   serial: b0:c0:90:ac:5c:8d
   width: 64 bits
   clock: 33MHz
   capabilities: pm msi pciexpress bus_master cap_list ethernet physical wireless
   configuration: broadcast=yes driver=rtl8821ae driverversion=4.4.0-57-generic firmware=N/A ip=10.26.8.222 latency=0 link=yes multicast=yes wireless=IEEE 802.11abgn
   resources: irq:130 ioport:d000(size=256) memory:df200000-df203fff
*-network
   description: Ethernet interface
   [...]

ash@earia:~$ lspci | grep 'Network\|Ethernet\|Wireless'
02:00.0 Network controller: Realtek Semiconductor Co., Ltd. RTL8821AE 802.11ac PCIe Wireless Network Adapter
03:00.1 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 12)

ash@earia:~$ modinfo iwlwifi | grep parm
parm:           swcrypto:using crypto in software (default 0 [hardware]) (int)
parm:           11n_disable:disable 11n functionality, bitmap: 1: full, 2: disable agg TX, 4: disable agg RX, 8 enable agg TX (uint)
parm:           amsdu_size_8K:enable 8K amsdu size (default 0) (int)
parm:           fw_restart:restart firmware in case of error (default true) (bool)
parm:           antenna_coupling:specify antenna coupling in dB (default: 0 dB) (int)
parm:           nvm_file:NVM file name (charp)
parm:           d0i3_disable:disable d0i3 functionality (default: Y) (bool)
parm:           lar_disable:disable LAR functionality (default: N) (bool)
parm:           uapsd_disable:disable U-APSD functionality (default: Y) (bool)
parm:           bt_coex_active:enable wifi/bt co-exist (default: enable) (bool)
parm:           led_mode:0=system default, 1=On(RF On)/Off(RF Off), 2=blinking, 3=Off (default: 0) (int)
parm:           power_save:enable WiFi power management (default: disable) (bool)
parm:           power_level:default power save level (range from 1 - 5, default: 1) (int)
parm:           fw_monitor:firmware monitor - to debug FW (default: false - needs lots of memory) (bool)

ash@earia:~$ modinfo rtl8821ae | grep parm
parm:           swenc:Set to 1 for software crypto (default 0)
parm:           ips:Set to 0 to not use link power save (default 1)
parm:           swlps:Set to 1 to use SW control power save (default 0)
parm:           fwlps:Set to 1 to use FW control power save (default 1)
parm:           msi:Set to 1 to use MSI interrupts mode (default 1)
parm:           debug:Set debug level (0-5) (default 0) (int)
parm:           disable_watchdog:Set to 1 to disable the watchdog (default 0)
parm:           int_clear:Set to 0 to disable interrupt clear before set (default 1)

Thanks in advance!

Ash Earia
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1 Answers1

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I am unaware of any method to deactivate 5 gHz channels from your wireless device. Perhaps we could study the driver code and deduce it, eventually.

However, you are interested in a quick solution because, ”... I'm probably going to overhaul my entire setup...”.

Network Manager includes a method to ignore certain devices. I suggest that you run:

sudo iwlist scan

Find the MAC address of the 5 gHz access points. Here is a scan example from my machine, as an example:

wlp3s0    Scan completed :
          Cell 01 - Address: XX:2B:B0:DC:45:XX
                    Channel:149
                    Frequency:5.745 GHz (Channel 149)
                    Quality=60/70  Signal level=-50 dBm  
                    Encryption key:on
                    ESSID:"GBR5"
                    Bit Rates:6 Mb/s; 9 Mb/s; 12 Mb/s; 18 Mb/s; 24 Mb/s
                              36 Mb/s; 48 Mb/s; 54 Mb/s
                    Mode:Master

Once you have the list, then edit /etc/NetworkManager/NetworkManager.conf to add a new line:

unmanaged-devices=mac:xx:2b:b0:dc:45:xx

You should add all the devices you wish to ignore separated by semi-colons. Here is the example from the man page:

unmanaged-devices=mac:00:22:68:1c:59:b1;mac:00:1E:65:30:D1:C4

I note that it evidently makes no difference whether the addresses are upper or lower case.

After making the edit, restart NM:

sudo service network-manager restart

Any improvement?

chili555
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