How Can I DiagnOSe Common Wifi No Access
The Function of Internet Addressing
In the realm of the Internet, individuals may be assigned a Public IPv4 address such as 161.184.248.70 or an IPv6 address like 2000:7d86:ccf9:4062:58a6:5369:f626:c23. A useful tool for checking these addresses is available at https://test-ipv6.com/. Nonetheless, trying to convey these addresses to those not well-versed in technology, or even identifying MAC addresses like 17:d5:96:cf:6c:f8, can be prone to error and become complex exceedingly fast. Moreover, this method does not provide any historical data (especially from previous issues).
Navigating the World Wide Web
In order to access a web page, like https://oreilly.org, the initial step involves accessing a DNS server to translate the host segment (oreilly) with the Top Level Domain (org) of the URL to an IP address, such as 87.94.61.238. Whenever your computer and browser make web requests, it sends its type along with it, 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
The Significance of Primary Gateways
By way of DHCP, your default gateway is typically an address that is configured automatically. You will be assigned a default gateway, such as 192.168.148.52 (with common endings being .1 or .254 based on the size of the scope), to which all of your computer’s traffic will be sent for onward routing. As for IPv6, a comprehensive examination is available at how-to-fix-ipv6-connectivity/ but checking on a Mac or Linux system can be done as follows:
command to check for IPv6 on Mac or Linux
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 192.168.148.52 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 fe80:1bc0:8332:ea33:6ac1%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): {239.250.109.89, 98.183.153.236}
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 17:d5:96:cf:6c:f8
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 00:8a:70:54:11:74
}
Resolving Connectivity Issues for Wired and Wireless Networks
When dealing with data transmission, it is important to troubleshoot connectivity issues for both wired and wireless (Wi-Fi) mediums used to send data to your router.
Troubleshooting Tips for Apple macOS / OSX Users
Regardless of the version of OSX/macOS being used, whether it’s 10.15.1, 11.5.8, or 12.0.5, there are various tools available for troubleshooting connectivity problems. However, manual actions and scripts do not provide a consistent set of correlated values over time. This is where automated remote troubleshooting becomes essential, particularly for teams that have adopted remote work and Work From Anywhere (WFA) practices.
Utilizing Pre-Installed Scripts for Assistance
One useful tool available on OSX/macOS is the sudo wdutil info command, which provides a dump of the current wireless settings to the CLI. It can also be configured to generate specific logs for troubleshooting purposes. Another comprehensive tool is the sysdiagnose function, which can generate a wide range of logs (although many are only relevant to wireless connectivity, similar to wdutil).
sudo nohup /usr/bin/sysdiagnose -u & can be used to run the tool in the background, while it writes logs to /var/tmp/<blah>.tar.gz. For an interactive run (despite minimal interaction), you can execute the commandsudo /usr/bin/sysdiagnose, which prompts a privacy warning. When not run in the background, it should open Finder in the appropriate location, or users can navigate to /var/tmp manually 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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