How Do You Troubleshoot Wifi Issues

The Fundamentals of Internet Addressing

In the world of the Internet, it’s common to have a Public IPv4 address, such as 215.38.232.124, or an IPv6 address, such as 2000:7f1b:874c:5ba5:5ab0:8598:439b:1269. You can verify this information by visiting https://test-ipv6.com/. However, when it comes to communicating these addresses to individuals who are not technologically savvy, or even attempting to recite MAC addresses like 0f:05:d4:9d:49:fb, mistakes can easily occur and things can get complex. Furthermore, this approach does not provide any historical data, especially related to past issues.

Navigating the Internet

When trying to access a webpage, such as https://larkin.com, you first connect to a DNS server to translate the host portion (larkin) combined with the Top Level Domain (com) of the URL to an IP address, like 24.102.20.115. Each time your computer and browser make a web request, they actually send information about their type. For example:
Mozilla/5.0 (Windows; U; Win 9x 4.90; SG; rv:1.9.2.4) Gecko/20101104 Netscape/9.1.0285

Understanding the Significance of Default Gateways

Your default gateway is typically an automatically assigned address through DHCP. It usually appears as a default gateway, like 10.62.99.147 (although they usually end in .1 or .254, depending on the scope size), and it is where your computer sends all its traffic to be routed onward. For IPv6, a detailed examination can be found at how-to-fix-ipv6-connectivity/, but you can verify it on a Mac or Linux by using:

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  10.62.99.147    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:b85d:813e:a64d:d17c%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): {208.111.63.112, 69.100.193.81}
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 0f:05:d4:9d:49:fb
  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 9a:a2:4e:25:2e:7a
}

Resolve Issues with Wired and Wireless Connections

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

Solutions for Apple macOS / OSX Users

No matter which version of OSX/macOS you’re currently using, whether it’s 10.15.5, 11.4.7, or 12.2.2, there are various tools available for troubleshooting. However, these manual actions and scripts fail to provide a set of correlated values over time. This is where automated remote troubleshooting becomes essential, especially for teams that have adopted remote work and Work From Anywhere (WFA).

Effective Built-in Scripts

A highly useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting. In addition, the more comprehensive sysdiagnose tool can be used to produce a wide range of logs, although much of it is only relevant to wireless at a specific point in time, similar to wdutil.

To run it in the background and have it write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively (although there isn’t much interaction), execute the command
sudo /usr/bin/sysdiagnose, which will trigger 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 direct Finder to the path. Just keep in mind that the file sizes are approximately 300MB, give or take.

Possibly Helpful Videos

Video	Title	Channel
	Wireless Packet Captures with Multiple Adapters Yer Yang WLPC Phoenix 2019	Wireless LAN Professionals
	Solving Wi-Fi problems in record time John Anderson WLPC US Phoenix 2017	Wireless LAN Professionals
	Real World Protocol Analysis Peter Mackenzie WLPC_EU Lisbon 2017	Wireless LAN Professionals
	Securing the World's Most Dangerous Wi-Fi Network Colin Vallance WLPC Phoenix 2020	Wireless LAN Professionals
	WiFiShark Fu Eddie Forero WLPC Phoenix 2019	Wireless LAN Professionals

Table 1.0 - Video Help