How Can I DiagnOSe Wifi Issues
The Functionality of Internet Addressing
Internet connectivity often involves obtaining a unique Public IPv4 address, such as 90.211.94.113, or an IPv6 address, like 2000:daa8:ccb8:3d70:e71d:f145:d4c6:f7b9. Verification of this connectivity can be done at https://test-ipv6.com/. Describing or referencing these addresses to individuals unfamiliar with technology, as well as mentioning MAC addresses like ee:4f:2a:21:ca:70, is prone to errors and becomes complex. In addition, it does not provide any historical data, which is especially critical when resolving previous issues.
Navigating the Internet
When attempting to reach a webpage, such as https://swift.name, the initial step is to contact a DNS server to convert the host section (swift) combined with the Top Level Domain (name) of the URL into an IP address, for instance, 28.182.212.52. In all web requests, your computer and browser transmit their types, for instance: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36
The Significance of Default Gateways
Typically, a default gateway is an address that is automatically configured via DHCP. For example, the default gateway could be 192.0.0.101 (commonly ending in .1 or .254 based on the scope size), and this is where your computer directs all traffic to be routed further. To learn how to resolve IPv6 connectivity issues, you can refer to how-to-fix-ipv6-connectivity/ or perform a verification on Mac or Linux 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 192.0.0.101 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:ec2e:b0b4:cdde:5333%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): {1.21.4.0, 58.96.61.217}
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 ee:4f:2a:21:ca:70
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 a2:40:5d:aa:ea:37
}
Resolving Wired and Wireless Connection Issues
When it comes to transmitting data to your router, you might be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Techniques for Apple macOS / OSX
Regardless of whether you are running OSX/macOS versions such as 10.12.6, 11.0.2, or 12.2.1, there are various troubleshooting tools available. However, the manual actions and scripts provide isolated values and lack the ability to track correlated values over time. This is where automated remote troubleshooting becomes crucial, especially for teams that prioritize remote work and Work From Anywhere (WFA).
Utilizing In-Built Scripts for Assistance
A valuable tool for OSX/macOS is sudo wdutil info, which provides a CLI dump of current wireless settings and can be configured to generate specific troubleshooting logs. Additionally, the sysdiagnose tool is even more comprehensive, as it can generate a wide range of logs (although much of it is related to wireless settings at a specific point in time, similar to wdutil).
By running sudo nohup /usr/bin/sysdiagnose -u &, the tool will run in the background and write logs to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively, you can execute sudo /usr/bin/sysdiagnose, which will prompt a privacy warning. When 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 or simply point Finder to the path. However, be cautious of the file sizes, which can be around 300MB.
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