How To Troubleshoot Wifi Issues
Explanation of Internet Addressing
When using the Internet, you are assigned a unique Public IPv4 address, such as 185.199.7.166, or an IPv6 address like 2000:6183:e9ab:a219:3c37:d2d:7752:7bac. There are tools, like https://test-ipv6.com/, to verify your address. Communicating these addresses to non-technical individuals can be quite complex and prone to errors. Unfortunately, there is also a lack of historical data available about these addresses.
The Process of Accessing Websites
When attempting to reach a specific web page, such as https://carter.info, you first access a DNS server to translate the URL’s host portion (in this case, carter) and its Top Level Domain (info) into an IP address, such as 140.238.161.207. Whenever your computer and browser make web requests, they include detailed information about their type, such as: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
Understanding the Significance of Default Gateways
Your default gateway is normally an address assigned automatically through DHCP, usually ending in .1 or .254. This gateway, represented by an address like 192.0.0.108, is where your computer sends all network traffic to be routed onwards. For those interested in setting up IPv6, there is an in-depth guide available at how-to-fix-ipv6-connectivity/. On Mac or Linux systems, you can verify this by using the following 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 192.0.0.108 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:b010:83ea:6a5d:1d22%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): {249.165.234.99, 1.46.43.34}
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 d0:d2:e7:30:c5:08
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 90:d3:bd:95:d9:aa
}
Resolving Issues with Wired and Wireless Connections
When sending data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Steps for Apple macOS / OSX
Regardless of the version of OSX/macOS you are using, whether it’s 10.13.3, 11.6.9, or 12.0.4, there are various 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 useful, especially for teams that adopt remote work and Work From Anywhere (WFA).
Pre-Installed Scripts That Offer Assistance
A very useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump to the CLI of current wireless settings and can also be set up to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can generate a wide range of logs, although much of it is point-in-time only related to wireless, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & will execute it in the background and write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (even though there isn’t much interaction), you can run sudo /usr/bin/sysdiagnose, which will display a privacy warning. If 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. However, be mindful of the file sizes, which are about 300MB more or less.
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