How Can I DiagnOSe Common Wifi Connectivity

How the System of Internet Addressing Functions

When using the Internet, you are assigned a Public IPv4 address such as 61.34.155.117 or an IPv6 address like 2000:bb16:92b1:63f9:33fa:66dd:72b:1fb1. This can be verified at https://test-ipv6.com/. However, attempting to convey these addresses, or even identify MAC addresses like 2b:0f:31:38:71:c3, can be prone to errors and quickly becomes complex, particularly for those who are less technically inclined. Furthermore, this method does not provide any historical data (especially from previous issues).

Navigating the World Wide Web

In order to access a web page such as https://boyle-ohara.biz, the first step involves reaching out to a DNS server to convert the host part (boyle-ohara) along with the Top Level Domain (biz) of the URL into an IP address like 237.206.147.155. Whenever a web request is made, your computer and browser also transmit their type, for example:
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A

The Significance of Deducing Default Gateways

Typically, your default gateway is an automatically configured address through DHCP. This leads to the assignment of a default gateway like 192.168.235.219 (usually terminating in .1 or .254 depending on the scope size), which is where all traffic from your computer is forwarded. For IPv6, a more comprehensive breakdown is available at how-to-fix-ipv6-connectivity/, although it can also be verified on Mac or Linux with:

IPv4 Routes and the Host IPv4 Route Table (inc. VPN)

netstat -rn -f inet | egrep -i "default|0/1|128.0/1"

0/1      172.18.12.193  UGScg  utun3
default  192.168.235.219    UGScg  en0
128.0/1  172.18.12.193  UGSc   utun3

Note: We are not just looking for the default but also for any VPN that overrides the public v4 address space.

IPv6 Routes and the Host IPv6 Route Table (inc. VPN)

netstat -rn -f inet6 | egrep -i "default|2000::/3"

If you have IPv6 active the above should return at least one route (as per below) via a known interface such as “en0 " on a Mac.

default   fe80:859a:9ac4:9218:d9cb%en0  UGcg   en0
default   fe80::%utun0                   UGcIg  utun0
default   fe80::%utun1                   UGcIg  utun1
default   fe80::%utun2                   UGcIg  utun2
2000::/3  utun3                          USc    utun3

Note: We are not just looking for the default but also for any VPN that overrides the public v6 address space.

Debugging DHCP for both IPv4 and IPv6

To get a look at the low level DHCP configuration (Mac/Linux):

ipconfig getpacket en0

...
domain_name_server (ip_mult): {164.164.35.147, 106.152.128.144}
end (none):
...

So, in the above we are not getting IPv6 DNS servers from the DHCPv4 reply but…

ipconfig getv6packet en0

DHCPv6 REPLY (7) Transaction ID 0x80940b Length 76
Options[4] = {
  CLIENTID (1) Length 14: DUID LLT HW 1 Time 668691856 Addr 2b:0f:31:38:71:c3
  DNS_SERVERS (23) Length 32: 2606:4700:4700::1111, 2001:4860:4860::8844
  DOMAIN_LIST (24) Length 0:  Invalid
  SERVERID (2) Length 10: DUID LL HW 1 Addr 72:f4:90:c4:c5:c0
}

Resolve Wired and Wireless Issues

When it comes to transmitting data to your router, you may be using a wired or wireless (Wi-Fi) medium at the physical and data layer.

Troubleshooting Tips for Apple macOS / OSX

No matter which version of OSX/macOS you are currently using, whether it’s 10.12.4, 11.1.3, or 12.1.2, there are various tools available for resolving issues. However, these manual actions and scripts lack the ability to provide a series of correlated values over time. This is where automated remote troubleshooting becomes essential, especially for teams that are embracing remote work and Work From Anywhere (WFA).

Useful Built-in Scripts

One extremely useful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI, and can also be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs (although much of it is point-in-time only in relation to wireless, similar to wdutil).

By running sudo nohup /usr/bin/sysdiagnose -u & in the background, logs will be written to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (although there isn’t much interaction), you can run
sudo /usr/bin/sysdiagnose, which will display a privacy warning. If not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp or use Finder with Cmd+Shift+G to point Finder to the path. Just be aware of the file sizes, which are approximately 300MB more or less.

Possibly Helpful Videos

Video	Title	Channel
	Real World Protocol Analysis Peter Mackenzie WLPC_EU Lisbon 2017	Wireless LAN Professionals
	The Importance of Broadcast/Multicast Filtering in Wi-Fi HD Arjan Koopen WLPC EU Budapest 2016	Wireless LAN Professionals
	Do You Have A Wired or Wireless Problem	Wireless LAN Professionals
	Securing the World's Most Dangerous Wi-Fi Network Colin Vallance WLPC Phoenix 2020	Wireless LAN Professionals
	Solving Wi-Fi problems in record time John Anderson WLPC US Phoenix 2017	Wireless LAN Professionals

Table 1.0 - Video Help