How Do You DiagnOSe Common Wifi No Access
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 or IPv6 address, such as 208.208.234.37 or 2000:55ed:c63:808e:41e8:f4c9:2b63:df8d. You can verify these addresses at https://test-ipv6.com/. However, conveying these addresses, or even mentioning MAC addresses like d5:cf:af:2e:cc:50, to those unfamiliar with technology can be prone to errors and quickly become complicated. Furthermore, this method does not provide any historical data, especially during previous issues.
Navigating the World Wide Web
Accessing a website like https://kiehn-hahn.biz involves the initial step of contacting a DNS server to convert the host portion (kiehn-hahn) combined with the Top Level Domain (biz) of the URL into an IP address, such as 156.213.219.25. Your computer and browser include their type in all web requests, for example: Mozilla/5.0 (Windows; U; Win 9x 4.90; SG; rv:1.9.2.4) Gecko/20101104 Netscape/9.1.0285
The Significance of Default Gateways
The default gateway is typically an automatically generated address through DHCP. It could be a default gateway like 192.168.27.228 (though typically ending in .1 or .254 depending on the scope size), and this is where your computer directs all its traffic to be routed further. For IPv6, you can find a detailed guide on how-to-fix-ipv6-connectivity/, but it can be verified on Mac or Linux using the following command:
[command line here]
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 192.168.27.228 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 fe80:751f:1432:cdc4:d65e%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): {190.35.74.182, 242.220.175.190}
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 d5:cf:af:2e:cc:50
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 c3:a2:6a:bc:5e:06
}
Fixing Connectivity Issues
When it comes to transmitting data to your router, you may encounter issues at the physical and data layer, whether you’re using a wired or wireless (Wi-Fi) connection.
Troubleshooting on Apple macOS / OSX
Regardless of whether you’re running OSX/macOS 10.11.3, 11.2.9, or 12.1.9, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes valuable, especially for teams that have embraced remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts
A useful tool on OSX/macOS is the sudo wdutil info, which provides a dump of current wireless settings to the CLI and can also be configured to generate specific troubleshooting logs. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs, although many of them are only relevant to wireless issues, similar to wdutil.
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can use sudo /usr/bin/sysdiagnose and it will display 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. Be mindful of the file sizes, which are typically around 300MB.
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