In reply to a post by Pheasant:

I think the router settings are generally fine, given that an iPhone can max the broadband throughput on speedtests.

But let’s see what the diagnostic from the iMac say…

yeah it is the imac, the question is; is it hardware or the os, and Big sur has had its fair share of wifi issues

@mysticLady can you try wifi via safe mode and see if the issue occurs again?

Edited by Taras (Fri 05-Nov-21 16:03:13)

I have just run Apple's network diagnostics tool and I now have a folder with a huge amount of files. I'm hoping somebody can help me work out what I now need to do

Can you also try safe mode as well. Third party software can cause issues too .

I already tried that. Also tried signing into a guest account. No speed difference.

ahh ok, so in theory we can discount 3rd party software.

Here's a sample of one (of around 50+) diagnostic files.

Conflicting Wi-Fi CC 0.001 Yes 16:26:19.452 Found conflicting country code(s) (gb)
'SKYVF8RT_2GEXT' — 44:a5:6e:93:bd:24 (FR)
Congested Wi-Fi Channel 0.005 Yes 16:26:19.441 Current channel (112) is congested (CCA = n/a)
Recommended 2.4GHz — 11
Recommended 5GHz — 161
Large PNL 0.002 Yes 16:26:19.425 Wi-Fi PNL count (14)
Uncommon DTIM Interval 0.001 Yes 16:26:19.407 DTIM interval is 0ms
Poor Wi-Fi Signal 0.001 Yes 16:26:19.404 Current network has poor signal (RSSI=-71dBm, SNR=21dB)
BT Connected Count 0.000 Yes 16:26:19.402 Connected Bluetooth device count (2)
BT Paired Count 0.044 Yes 16:26:19.357 Paired Bluetooth device count (3)
Custom Web Proxy 0.001 Yes 16:26:19.356 Detected custom web proxy settings
Custom IPv6 0.001 Yes 16:26:19.354 Wi-Fi is using 'Link Local' for IPv6
Primary IPv6 is Wi-Fi 0.002 No 16:26:19.350 None
IPv6 Assigned 0.001 No 16:26:19.346 Wi-Fi does not have IPv6 assigned
Ping6 AWDL 0.001 No 16:26:11.424 Could not ping AWDL ((null) / 0.00ms / BE / 64 bytes / w=0.000000s / c=0)
Ping WAN 1.006 No 16:26:08.322 Could not ping DNS server (17.254.0.22 / 0.00ms / BE / 68 bytes / i=0.100000s / W=1.600000s / t=1.600000s / c=1)
Curl Apple 0.508 Yes 16:25:36.388 Could curl 'https://captive.apple.com'
Reach Apple 2.567 Yes 16:25:36.388 Could reach 'www.apple.com'
Ping6 AWDL 2.567 No 16:25:36.388 Could not ping AWDL ((null) / 0.00ms / BE / 64 bytes / w=0.000000s / c=0)
Resolve DNS 2.568 Yes 16:25:36.388 Could resolve 'captive.apple.com'
Ping WAN 3.587 No 16:25:36.388 Could not ping DNS server (17.254.0.22 / 0.00ms / BE / 68 bytes / i=0.100000s / W=1.600000s / t=1.600000s / c=1)
Ping WAN 3.893 Yes 16:25:36.388 Could ping DNS server (192.168.1.1 / 3.17ms / BE / 69 bytes / i=0.100000s / W=1.600000s / t=1.600000s / c=1)
Ping LAN 3.902 Yes 16:25:36.388 Could ping router (192.168.1.1 / 7.89ms / VI / 66 bytes / i=0.100000s / W=1.600000s t=1.600000s / c=1)
Ping LAN 3.902 Yes 16:25:36.388 Could ping router (192.168.1.1 / 8.08ms / VO / 67 bytes / i=0.100000s / W=1.600000s t=1.600000s / c=1)
Ping LAN 3.902 Yes 16:25:36.388 Could ping router (192.168.1.1 / 7.22ms / BK / 65 bytes / i=0.100000s / W=1.600000s t=1.600000s / c=1)
Ping LAN 3.902 Yes 16:25:36.388 Could ping router (192.168.1.1 / 6.93ms / BE / 64 bytes / i=0.100000s / W=1.600000s t=1.600000s / c=1)
Ping LAN 4.398 Yes 16:25:36.388 Could ping router (192.168.1.1 / 2.00ms / VO / 73 bytes / i=0.100000s / W=0.200000s t=1.600000s / c=6)
Ping LAN 4.399 Yes 16:25:36.388 Could ping router (192.168.1.1 / 2.03ms / BK / 71 bytes / i=0.100000s / W=0.200000s t=1.600000s / c=6)
Ping LAN 4.399 Yes 16:25:36.388 Could ping router (192.168.1.1 / 2.02ms / BE / 70 bytes / i=0.100000s / W=0.200000s t=1.600000s / c=6)
Ping LAN 4.466 Yes 16:25:36.388 Could ping router (192.168.1.1 / 1.47ms / VI / 72 bytes / i=0.100000s / W=0.200000s t=1.600000s / c=6)

2 lines worth looking at

Poor Wi-Fi Signal 0.001 Yes 16:26:19.404 Current network has poor signal (RSSI=-71dBm, SNR=21dB)

Congested Wi-Fi Channel 0.005 Yes 16:26:19.441 Current channel (112) is congested (CCA = n/a)

So you need to access your router and change the wifi channels being used to

Recommended 2.4GHz — 11
Recommended 5GHz — 161

In reply to a post by MysticLady:

Here's a sample of one (of around 50+) diagnostic files.
Ping WAN 1.006 No 16:26:08.322 Could not ping DNS server (17.254.0.22 / 0.00ms / BE / 68 bytes / i=0.100000s / W=1.600000s / t=1.600000s / c=1)

Apple heads
Any reason why it needs to use apple dns servers...

I would suspect it's just doing some sort of diagnostic *test* against Apple DNS servers. Anyway that won't affect wifi throughput.

Still waiting for the results of option-click on the wifi. On my machine for example, I get:

Channel: 36 (5 GHz, 80 MHz)
RSSI: -55 dBm
Noise: -92 dBm
Tx Rate: 434 Mbps
PHY Mode: 802.11ac

Here are the other files in the diagnostics report:

sw_vers.txt
3bars.txt
additional.log
arp.txt
awdl_status.txt
bluetooth_status.txt
BluetoothPacketLog.pklg
bonjour_records.txt
com.apple.airport.preferences.plist
com.apple.Bluetooth.plist
com.apple.network.eapolclient.configuration.plist
com.apple.wifi.known-networks.plist
com.apple.wifi.recent-networks.json
com.apple.wifi.syncable-networks.legacy.plist
com.apple.wifi.syncable-networks.plist
CommunityFibre10Gb_7DC47-diagnostics.txt
configd-store.plist
CoreCapture
debug-log.txt
diagnostics-configuration.txt
diagnostics-connectivity.txt
diagnostics-environment.txt
easyperf_airportd.txt
easyperf_WiFiAgent.txt
en1_tcpdump.pcap
event_history.txt
footprint_airportd.txt
footprint_WiFiAgent.txt
heap_airportd.txt
heap_WiFiAgent.txt
ifconfig.txt
jetsam_priority.txt
leaky_ap_stats.txt
ndp.txt
netstat-POST.txt
netstat-PRE.txt
network_status.txt
ping.txt
security.txt
sysdiagnose_2021.11.05_16-27-23+0000_macOS_iMac18-3_20G224.tar.gz
system_profiler.spx
traceroute.txt
vmmap_airportd.txt
vmmap_WiFiAgent.txt
wifi_datapath-POST.txt
wifi_datapath-PRE.txt
wifi_scan.txt
wifi_status.txt
wifi-11-05-2021__16/25/34.562.log.tgz
wifi-11-05-2021__16/25/35.994.log.tgz
wifi-11-05-2021__16/25/40.268.log.tgz
wifi-11-05-2021__16/25/48.064.log.tgz
wifi-11-05-2021__16/26/22.330.log.tgz
wifi-11-05-2021__16/26/25.143.log.tgz
wifi.log.0.bz2
wifi.log.tgz
wifivelocity_logarchive.log.tgz
WirelessRadioManager.log.tgz
zprint.txt