How Can I Troubleshoot Wifi No Access

Understanding IP Addressing on the Internet

When connecting to the Internet, you are assigned a Public IPv4 address, such as 125.77.64.149, or an IPv6 address, like 2000:2614:edbb:3cd3:27d2:18f9:760a:e9fa. These addresses can be verified at https://test-ipv6.com/, but explaining them to non-technical individuals, or even referencing MAC addresses like fe:40:b8:58:4b:8d, can be prone to errors and complex. Moreover, this method does not provide any historical data, particularly when addressing previous issues.

Navigating the World Wide Web

When attempting to access a website, such as https://brekke.com, you must first contact a DNS server to convert the host portion (brekke) combined with the Top Level Domain (com) of the URL into an IP address, for example, 251.138.28.72. With all web requests, your computer and browser send their type, such as:

Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0

The Significance of Default Gateways

Typically, your default gateway is an address automatically configured through DHCP, such as 10.209.214.106 (although they generally end in .1 or .254, depending on the scope size). This is where your computer sends all its traffic to be routed onwards. For IPv6, in-depth instructions can be found at /blog/how-to-fix-ipv6-connectivity/; however, you can verify on Mac or Linux by using:

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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  10.209.214.106    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   fe80:27a1:cadd:a8ff:c7e9%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): {62.176.177.247, 76.202.66.253}
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 fe:40:b8:58:4b:8d
  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 e1:70:38:27:3b:ff
}

Resolving Connectivity Issues for Wired and Wireless Networks

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

Troubleshooting Techniques for Apple macOS / OSX

Regardless of the version of OSX/macOS being used, whether it’s 10.12.8, 11.2.7, or 12.2.2, there are various tools available for troubleshooting purposes. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes incredibly useful, especially for teams that are remote work-oriented and embrace the concept of Work From Anywhere (WFA).

Utilizing Built-in Scripts for Assistance

One valuable tool on OSX/macOS is “sudo wdutil info,” which provides a dump of current wireless related settings to the CLI and can be configured to generate specific logs for troubleshooting. Additionally, the “sysdiagnose” tool can be used to generate a wide range of logs, although many of them are point-in-time only in relation to wireless, similar to wdutil.

Running “sudo nohup /usr/bin/sysdiagnose -u &” in the background will write logs to “/var/tmp/.tar.gz” for you. If you prefer to run it interactively, you can run “sudo /usr/bin/sysdiagnose,” which will open Finder in the correct location or allow you to navigate to “/var/tmp” or use Finder with Cmd+Shift+G to point to the path. Just keep in mind the file sizes, which are around 300MB more or less.

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