How To Troubleshoot Common Wifi No Access
The Functioning of Internet Addressing
When using the Internet, individuals may be assigned a Public IPv4 address, such as 87.71.36.20, or an IPv6 address, like 2000:d4d4:185d:a4af:63fd:b231:965e:cdd3. This information can be verified at https://test-ipv6.com/. However, for those unfamiliar with technical terminology, conveying these addresses, or even referencing MAC addresses like 4a:cd:a7:18:4e:f7, can be prone to errors and becomes complex. Additionally, it does not provide any historical data, particularly regarding past issues.
Navigating the World Wide Web
When attempting to visit a web page, such as https://orn.net, an initial step involves accessing a DNS server to translate the host portion (orn) combined with the Top Level Domain (net) of the URL to an IP address, like 92.198.122.220. Additionally, the computer and browser transmit their types with all web requests, for example: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A
Understanding the Significance of Default Gateways
Typically, a default gateway is an automatically configured address received via DHCP. This default gateway, such as 10.78.15.152 (commonly ending in .1 or .254 based on the scope size), is where a computer sends all traffic to be routed onwards. For IPv6, comprehensive information is available in the article how-to-fix-ipv6-connectivity/. Users can also verify this information on Mac or Linux 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 10.78.15.152 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:ff22:8e26:73c0:9951%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): {178.33.123.237, 39.109.61.210}
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 4a:cd:a7:18:4e:f7
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 7f:60:6a:1a:bb:ca
}
Solutions for Wired and Wireless Connectivity Issues
When transmitting data to your router, you may encounter connectivity issues at the physical and data layer, whether you are using a wired or wireless (Wi-Fi) medium.
Tips for Troubleshooting on Apple macOS / OSX
Regardless of the version of OSX/macOS you are using, whether it’s 10.15.9, 11.1.5, or 12.1.5, there are several 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 invaluable, particularly for teams that embrace remote work and Work From Anywhere (WFA).
Useful 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 logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a variety of logs, although much of it is only related to wireless settings at a particular point in time, similar to wdutil.
To run sysdiagnose in the background and generate logs in /var/tmp/<blah>.tar.gz, you can use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can use the command sudo /usr/bin/sysdiagnose, which will give a privacy warning. When running it in the foreground, it will open Finder in the correct location, or you can navigate to /var/tmp or use Finder with Cmd+Shift+G to specify the path. Keep in mind that the file sizes are approximately 300MB.
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