How To Check MacOS Issues
Understanding Internet Addressing
When using the internet, you are assigned a Public IPv4 address such as 19.115.147.91 or an IPv6 address like 2000:2605:fc1b:f8c8:91c2:7494:b112:f14d. This information can be verified at https://test-ipv6.com/. However, conveying these addresses, as well as MAC addresses like 13:3a:cf:ae:00:a8, to individuals who are not technically inclined can be prone to errors and confusing. Moreover, this method does not provide historical data, especially regarding past issues.
Navigating the World Wide Web
When attempting to access a website, such as https://towne.com, you start by reaching out to a DNS server to convert the host portion (towne) in combination with the URL’s Top Level Domain (com), to an IP address like 181.88.153.204. Whenever your computer and web browser make web requests, they include information about their type, such as Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16.
The Significance of Default Gateways
Typically, your default gateway is automatically configured through DHCP and you receive a default gateway like 172.22.206.167 (usually ending in .1 or .254, depending on the scope size). This is where your computer sends all of its traffic to be routed further. For IPv6, an in-depth exploration is available at how-to-fix-ipv6-connectivity/, but you can also verify on Mac or Linux 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 172.22.206.167 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 fe80:57fd:29e6:cf42:e56e%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): {175.129.133.76, 174.68.110.63}
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 13:3a:cf:ae:00:a8
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 f6:0f:5f:29:11:c7
}
Resolve Connectivity Issues for Wired and Wireless Networks
When it comes to transmitting data at the physical and data layer, you have the option of using either a wired or wireless (Wi-Fi) medium to send the data to your router.
Troubleshooting on Apple macOS / OSX
Regardless of the version of OSX/macOS you are using, whether it’s 10.12.4, 11.5.2, or 12.1.9, 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 valuable, especially for teams embracing remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts for Assistance
A useful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a comprehensive set of logs, although much of it is point-in-time information in relation to wireless, similar to wdutil.
To run the sysdiagnose tool in the background and write logs to /var/tmp/<blah>.tar.gz, you can use the command sudo nohup /usr/bin/sysdiagnose -u &. Alternatively, for interactive use, you can run sudo /usr/bin/sysdiagnose, which will provide 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 approximately 300MB.
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