How Can I Troubleshoot Common Wifi No Access
Understanding Internet Addressing
When using the Internet, you will be assigned a Public IPv4 address such as 156.242.127.166 or an IPv6 address like 2000:a85d:b9d3:1d0d:d153:20cf:bc93:ad9. This assignment can be verified by visiting https://test-ipv6.com/. Communicating these addresses, or even referring to MAC addresses like e1:47:07:96:5f:00, can be complex and error-prone, especially for those not well-versed in technology. Moreover, this method does not provide any historical data, which can be crucial when troubleshooting past issues.
Navigating the World Wide Web
When trying to access a website such as https://white-thiel.com, your computer first connects to a DNS server to convert the host portion (white-thiel) and the Top Level Domain (com) of the URL into an IP address, for example, 238.239.68.43. Your computer and browser also include its type in all web requests, such as Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)
Significance of Default Gateways
The default gateway, usually assigned automatically via DHCP, serves as the access point for all outbound traffic from your computer. This gateway, like 192.168.181.107 (although typically ending in .1 or .254 depending on the scope size), is where your computer sends all its traffic to be routed onwards. For IPv6, detailed information is available in our article how-to-fix-ipv6-connectivity/. On Mac or Linux, you can check this 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 192.168.181.107 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 fe80:5c88:ce0:2390:ce2b%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): {255.28.236.189, 189.220.99.209}
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 e1:47:07:96:5f:00
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 48:b3:cc:5f:2c:a7
}
Resolving Issues with Wired and Wireless Connections
When it comes to transferring data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX Users
No matter which version of OSX/macOS you are currently using, be it 10.15.3, 11.2.5, or 12.0.3, there exist a variety of tools for troubleshooting. However, the manual actions and scripts available do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams that have adopted remote work and Work From Anywhere (WFA).
Utilizing Pre-installed Scripts for Assistance
One immensely useful tool on OSX/macOS is the sudo wdutil info, which provides a dump to the CLI of current wireless settings and can also be configured to generate specific troubleshooting logs. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant to wireless settings at a specific point in time, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & will execute the tool in the background, writing logs to /var/tmp/<blah>.tar.gz. For an interactive run (although there is minimal interaction involved), you can execute sudo /usr/bin/sysdiagnose, which will prompt a 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 be mindful of the file sizes, which can be approximately 300MB.
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