How To Troubleshoot Mac Issues
The Fundamentals of Internet Addressing
When using the Internet, individuals may have a unique Public IPv4 address, such as 202.14.206.226, or an IPv6 address, like 2000:6824:3716:bf19:e519:8b7a:7343:6be4. These addresses can be verified through https://test-ipv6.com/. However, explaining and communicating these addresses, as well as MAC addresses like c6:64:82:8f:16:2e, can be complex and error-prone, especially for those with limited technical knowledge. This method also does not provide any historical data, particularly during past difficulties.
Navigating the World Wide Web
Accessing a web page, such as https://rau.name, initially involves connecting to a DNS server to convert the URL’s host portion (rau) combined with the Top Level Domain (name) into an IP address like 222.79.123.66. In all web requests, your computer and browser send their type, for instance Mozilla/5.0 (Windows; U; Win 9x 4.90; SG; rv:1.9.2.4) Gecko/20101104 Netscape/9.1.0285
Understanding the Significance of Default Gateways
The default gateway is usually an address automatically configured through DHCP. It typically ends in .1 or .254, depending on the scope size, for example, 192.0.0.92. This is where your computer directs all its traffic for further routing. For detailed instructions on verifying default gateways for IPv6, refer to how-to-fix-ipv6-connectivity/. On Mac or Linux, this can be checked using:
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 192.0.0.92 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:ce3b:c38:1897:9969%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): {7.179.215.160, 27.232.17.0}
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 c6:64:82:8f:16:2e
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 cc:ff:e4:11:0c:f0
}
Resolving Connectivity Issues in Wired and Wireless Networks
When it comes to transferring data to your router, the choice of using a wired or wireless (Wi-Fi) medium at the physical and data layer can pose some challenges.
Troubleshooting Solutions for Apple macOS / OSX Users
No matter which version of OSX/macOS you are currently running - be it 10.15.8, 11.1.6, or 12.0.5 - there are various troubleshooting tools available to help. However, these manual actions and scripts fail to provide a set of interconnected values over time. This is where automated remote troubleshooting becomes invaluable, particularly for teams that have embraced remote work and the Work From Anywhere (WFA) concept.
In-Built Tools for Assistance
One particularly useful tool for OSX/macOS users is the sudo wdutil info command, which provides a detailed dump of the current wireless settings to the CLI and can also be configured to generate specific troubleshooting logs. Moreover, the sysdiagnose tool offers a more comprehensive solution by generating a wide range of logs (although many are only relevant to wireless settings at a specific point in time, much like wdutil).
To run sysdiagnose in the background and have it write logs to /var/tmp/<blah>.tar.gz, you can use the command sudo nohup /usr/bin/sysdiagnose -u &. Alternatively, you can run it interactively by using sudo /usr/bin/sysdiagnose, although it will prompt a privacy warning. When not run in the background, it should open Finder in the appropriate location, or you can navigate to /var/tmp via Finder using Cmd+Shift+G. Keep in mind that the file sizes are typically around 300MB.
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