How Do You Troubleshoot Wifi No Access
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 245.94.166.3, or an IPv6 address, like 2000:7a74:ecef:3d35:4602:f428:66f1:ce36. You can verify this information at https://test-ipv6.com/. However, attempting to convey these addresses to non-technical individuals or even referencing MAC addresses, such as 7a:4b:e1:a7:ef:80, can be prone to errors and become complex. Furthermore, you will not have access to historical data, particularly when previous issues occurred.
Navigating the World Wide Web
When accessing a web page, such as https://paucek.com, you first reach out to a DNS server to translate the host portion (paucek) combined with the Top Level Domain (com) of the URL to an IP address, such as 248.117.26.237. Your computer and web browser include its type with every web request, 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 usually an automatically configured address via DHCP. It might look something like 192.0.0.209 (typically ending in .1 or .254 depending on the scope size), and it is where your computer sends all of its traffic to be routed onwards. For IPv6, you can find more detailed information on how-to-fix-ipv6-connectivity/, but you can check on a Mac or Linux system with:
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 192.0.0.209 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:d22f:79aa:25ae:2452%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): {211.80.165.249, 202.53.65.10}
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 7a:4b:e1:a7:ef:80
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 d2:78:1d:dc:b3:17
}
Resolving Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
No matter which version of OSX/macOS you are currently running, whether it’s 10.13.1, 11.1.6, or 12.2.4, there are various tools available for troubleshooting. Unfortunately, the manual actions and scripts provided do not offer a set of correlated values over time. This is where automated remote troubleshooting becomes crucial, especially for teams that are embracing remote work and the Work From Anywhere (WFA) concept.
Utilizing Pre-Installed Scripts for Assistance
A particularly 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. Moreover, the more comprehensive sysdiagnose tool can be used to generate a wide array of logs, although many of them are only relevant to wireless settings at a specific time, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & will execute the tool in the background and generate logs in /var/tmp/<blah>.tar.gz. If you prefer to run it interactively (although there isn’t much interaction involved), you can use sudo /usr/bin/sysdiagnose and it will provide a privacy warning. If not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp or use Finder with Cmd+Shift+G to locate the path. It’s important to note that the file sizes are approximately 300MB.
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