How Can I Understand Apple Issues
Explanation of Internet Addressing Systems
When using the Internet, it is common to have a Public IPv4 address such as 8.32.86.32 or an IPv6 address like 2000:6a24:503d:cb1b:3ca7:f57c:d880:736b. Verification of these addresses can be done using https://test-ipv6.com/. Communicating or identifying MAC addresses like 56:b1:ae:ec:d8:a5 can be prone to errors and can become quite complex. Moreover, this approach lacks historical data, which is especially important when troubleshooting past issues.
Navigating Websites
Accessing a website like https://king.io involves initial contact with a DNS server to convert the host portion (king) plus the Top Level Domain (io) of the URL to an IP address, such as 191.101.151.170. Every web request sent by your computer and browser includes its type, for example, Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
Significance of Default Gateways
In most cases, your default gateway is automatically assigned through DHCP. It typically takes the form of a default gateway like 192.0.0.120 (although they usually end in .1 or .254 depending on the scope size), and serves as the central point for routing all your computer’s traffic. For IPv6, a detailed guide can be found at how-to-fix-ipv6-connectivity/, and checking on Mac or Linux can be accomplished 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 192.0.0.120 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 fe80:9182:2af1:39b8:5de5%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): {192.32.147.129, 88.109.178.167}
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 56:b1:ae:ec:d8:a5
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 71:80:ec:6d:a8:d9
}
Resolving Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting on Apple macOS / OSX
Regardless of the version of OSX/macOS you are using, whether it is 10.15.6, 11.4.1, or 12.0.5, 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 essential, especially for teams that are adapting to remote work and Work From Anywhere (WFA) practices.
Useful Built-in Scripts
One highly beneficial tool on OSX/macOS is sudo wdutil info, which provides a dump to the CLI of current wireless settings and can 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 relates to wireless settings and is only recorded at a specific point in time, similar to wdutil.
By running sudo nohup /usr/bin/sysdiagnose -u &, you can run sysdiagnose in the background and it will write logs to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively, you can execute sudo /usr/bin/sysdiagnose and it will trigger a privacy warning. Running it in the foreground should open Finder in the correct location, or you can navigate to /var/tmp or use Finder with Cmd+Shift+G to point to the path. However, be mindful of the file sizes, which are approximately 300MB.
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