How Can I Troubleshoot Mac Issues
The Function of Internet Addressing
When using the Internet, you may possess a Public IPv4 address such as 247.174.53.62, or an IPv6 address like 2000:8c0a:3562:7377:d321:d5a9:73aa:8ccc. You can verify this at https://test-ipv6.com/. However, attempting to communicate these addresses to individuals who are not technologically inclined, or even mentioning MAC addresses like 25:2b:a9:79:fe:d0, can be prone to errors and rather complicated. Moreover, this method does not provide any historical data (especially related to past issues).
Navigating Through the Internet
In order to access a website such as https://boyle.com, your computer first contacts a DNS server to convert the host portion (boyle) paired with the Top Level Domain (com) of the URL, to an IP address like 103.113.72.245. Your computer and browser send their information with every web request, for example: Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
Understanding the Significance of Default Gateways
The default gateway is usually an address that is configured automatically via DHCP. Your computer acquires a default gateway such as 192.0.0.204 (although they typically end in .1 or .254 depending on the size of the scope), and this is where all your computer’s traffic is sent for further routing. For IPv6, detailed instructions can be found at how-to-fix-ipv6-connectivity/, but on Mac or Linux, the default gateway 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 192.0.0.204 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 fe80:28ad:c45e:955:218a%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): {69.159.74.165, 134.244.176.154}
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 25:2b:a9:79:fe:d0
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 03:c7:be:b7:63:8c
}
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.
Tips for Troubleshooting on Apple macOS / OSX
No matter which version of OSX/macOS you are currently using - whether it’s 10.15.2, 11.6.2, or 12.3.6 - there are various tools available for identifying and fixing issues. However, these manual actions and scripts do not provide a set of correlated values over time, which is where automated remote troubleshooting becomes essential. This is particularly true for teams that have adopted remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the command line interface and can also be configured to generate specific troubleshooting logs. Furthermore, the sysdiagnose tool can be used to produce a wide range of logs, although many of them are only relevant to wireless settings at a specific point in time, similar to wdutil.
To run it in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. Alternatively, if you prefer to run it interactively, use the command sudo /usr/bin/sysdiagnose and it will display 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. Keep in mind that the file sizes are around 300MB.
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