How Do You Test MacOS Issues
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address such as 175.74.35.241 or an IPv6 address like 2000:1c74:dc4:5315:38c7:cdfe:7e73:d4b9. These addresses can be verified at https://test-ipv6.com/. However, explaining and sharing these addresses, as well as MAC addresses like b9:eb:fd:64:1c:58, with individuals who are not tech-savvy can lead to errors and confusion. Furthermore, it does not provide any historical data, particularly for past issues.
Navigating the World Wide Web
Accessing a webpage such as https://mertz.net involves initially connecting to a DNS server to convert the host portion (mertz) and the Top Level Domain (net) of the URL into an IP address like 91.143.149.133. Moreover, your computer and browser disclose their type with every web request, 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
The default gateway is typically an automatically configured address through DHCP. You are assigned a default gateway, such as 10.81.31.163 (usually ending in .1 or .254 based on the scope size), where your computer forwards all its traffic for routing. For IPv6, detailed guidance is available at how-to-fix-ipv6-connectivity/, and on Mac or Linux, this can be verified 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 10.81.31.163 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:e52d:d9d2:95a:dce%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): {179.138.63.167, 162.117.198.110}
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 b9:eb:fd:64:1c:58
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 7a:7a:82:d5:64:29
}
Troubleshooting Options for 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.
Solutions for Apple macOS / OSX
Regardless of your version of OSX/macOS, whether it’s 10.15.2, 11.2.2, or 12.2.8, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes useful, particularly for teams that embrace remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
A very useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can also be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant to wireless at a specific point in time, similar to wdutil.
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can use the command 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 Cmd+Shift+G in Finder. Keep in mind that the file sizes are approximately 300MB.
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