How Do You Troubleshoot Wifi Connectivity

Understanding the Function of Internet Addressing

When using the Internet, your device may have a Public IPv4 or IPv6 address, such as 68.53.252.8 or 2000:1a72:1984:e279:989b:2056:85e1:34d9. It is possible to verify this at https://test-ipv6.com/. However, conveying these addresses to individuals who are not tech-savvy, or even mentioning MAC addresses like f4:c5:d3:b1:13:69, can quickly become complicated and prone to errors. Moreover, this method does not provide any historical data, especially regarding past issues.

Navigating the World Wide Web

When attempting to reach a website such as https://hartmann.io, the initial step involves contacting a DNS server to convert the host portion (hartmann) combined with the Top Level Domain (io) of the URL into an IP address, like 21.24.74.179. Each web request from your computer and browser includes its type, as showcased in the example below:

Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)

The Significance of Default Gateways

Typically, your default gateway is assigned automatically via DHCP and takes the form of an address like 192.168.205.245 (although they often end in .1 or .254 based on the scope size). This is where all the traffic from your computer is directed for further routing. For in-depth information on configuring IPv6, visit how-to-fix-ipv6-connectivity/. Alternatively, you can perform a check on Mac or Linux using the following command:

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  192.168.205.245    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   fe80:483d:cf5d:fd14:1628%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): {174.136.108.171, 96.126.119.235}
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 f4:c5:d3:b1:13:69
  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:6f:77:cc:ea:53
}

Fixing Connectivity Issues for Wired and Wireless Networks

When it comes to sending 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

Regardless of which version of OSX/macOS you are using, whether it’s 10.15.7, 11.0.7, or 12.0.1, there are various tools available for troubleshooting. However, these tools do not provide a series of correlated values over time, making automated remote troubleshooting especially valuable for remote teams and those embracing Work From Anywhere (WFA).

Useful Built-in Scripts

One tool that can be incredibly helpful on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI and can also generate specific logs for troubleshooting. Another comprehensive tool is the sysdiagnose tool, capable of generating a wide range of logs, although much of it is only relevant to wireless at a specific point in time, similar to wdutil.

Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively, you can use
sudo /usr/bin/sysdiagnose while being mindful of the privacy warning. When not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp using Finder with Cmd+Shift+G. Just keep in mind that the file sizes are around 300MB.

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