How To DiagnOSe Common Wifi No Access
Understanding Internet Address Allocation
When connecting to the Internet, you are assigned a Public IPv4 address such as 193.249.154.245 or an IPv6 address like 2000:996e:48c2:d7e2:2c63:91dd:89c2:5e92. The allocation can be verified using https://test-ipv6.com/. However, communicating these addresses, as well as MAC addresses like 77:54:fc:f6:f7:29, is prone to errors and can become complex. Furthermore, it does not provide any historical data, particularly from previous issues.
Navigating the World Wide Web
Accessing a web page such as https://simonis-swaniawski.com involves the initial use of a DNS server to convert the URL’s host portion (simonis-swaniawski) combined with its Top Level Domain (com) into an IP address like 223.54.116.146. When making web requests, your computer and browser also sends its type, for example: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36
Understanding the Significance of Default Gateways
The default gateway is typically an automatically configured address through DHCP, such as 192.0.0.104 (although they generally end in .1 or .254 depending on the scope size). This is the location where your computer sends all its traffic to be forwarded. For IPv6, a detailed analysis of this process can be found in how-to-fix-ipv6-connectivity/. Additionally, it can be checked on Mac or Linux using the 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 192.0.0.104 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 fe80:65c7:fe8b:7342:8ace%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): {240.208.24.248, 166.120.14.251}
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 77:54:fc:f6:f7:29
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 42:fb:84:d5:3b:b1
}
Fixing Connectivity Issues for Wired and Wireless Networks
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
Regardless of the version of OSX/macOS you are using - whether it’s 10.13.3, 11.5.5, or 12.1.8 - there are numerous tools available for troubleshooting. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes extremely valuable, particularly for teams that have embraced remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One extremely useful tool on OSX/macOS is the sudo wdutil info, which outputs current wireless settings to the CLI and can also generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs, although many are specific to a particular point in time related to wireless, similar to wdutil.
To run it in the background and write logs to /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 sudo /usr/bin/sysdiagnose, which will give a privacy warning and open Finder in the correct location. Just be mindful of the large file sizes of around 300MB.
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