How To Troubleshoot MacOS Issues
Understanding Internet Addressing
When using the Internet, you are assigned a public IPv4 address such as 143.96.197.30 or an IPv6 address like 2000:9903:16c4:e7aa:a055:39b8:3028:75ce. You can verify this information by visiting https://test-ipv6.com/. However, for individuals who are not tech-savvy, communicating these addresses or even referencing MAC addresses like c2:16:e2:4c:ac:cc can be prone to mistakes and overwhelming. Furthermore, this does not provide any historical data, particularly from previous incidents.
Navigating the World Wide Web
When accessing a website such as https://leffler-klocko.com, the first step is to connect to a DNS server to convert the host part (leffler-klocko) in combination with the Top Level Domain (com) of the URL to an IP address like 27.210.73.116. Your computer and browser actually sends its type with all web requests, for example: Mozilla/5.0 (Windows; U; Win 9x 4.90; SG; rv:1.9.2.4) Gecko/20101104 Netscape/9.1.0285
Significance of Default Gateways
By default, your gateway is automatically configured through DHCP. You receive a default gateway like 192.0.0.134 (although they typically end in .1 or .254 depending on the scope size), and this is where your computer directs all its traffic to be routed onward. For IPv6, we have a detailed explanation available at how-to-fix-ipv6-connectivity/. Additionally, you can verify this 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 192.0.0.134 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 fe80:9e2e:6c2d:13d0:4253%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): {129.188.251.182, 131.186.96.33}
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 c2:16:e2:4c:ac:cc
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 10:c0:d0:0e:16:75
}
How to Resolve Connectivity Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you have the option of using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX Users
Whether you are running OSX or macOS, whether it’s version 10.15.5, 11.2.9, or 12.2.2, 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 remote troubleshooting tools become essential, especially for teams engaged in remote work and Work From Anywhere (WFA) setups.
Utilizing the In-Built Scripts for Assistance
One of the most useful tools for OSX/macOS users is sudo wdutil info, which provides a dump of current wireless settings to the command-line interface (CLI) and can also be configured to generate specific logs for troubleshooting purposes. Additionally, the sysdiagnose tool offers a more comprehensive approach, generating a wide range of logs (although most are only relevant at a specific point in time, similar to wdutil).
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz. For an interactive run, you can use sudo /usr/bin/sysdiagnose, which will trigger a privacy warning. When not run in the background, it should open Finder in the correct location, allowing you to navigate to /var/tmp. Just be mindful of the file sizes, which can be around 300MB or more.
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