How Can I Understand Apple Connectivity
The Functionality of IP Addresses
When using the Internet, you are assigned a unique identifier known as a Public IPv4 address, such as 149.83.41.62, or an IPv6 address, such as 2000:1c9b:46ee:682e:3dda:10a1:f229:1274. The website https://test-ipv6.com/ is useful for verifying these addresses. However, for those who are not technically inclined, conveying these addresses, or even MAC addresses like 5d:0a:dc:f3:86:a5, can be prone to errors and become complex. Moreover, this method does not provide any historical data, especially in cases of past issues.
Navigating the Internet
When attempting to access a webpage like https://wisoky-hills.name, the process begins by reaching out to a DNS server to convert the host portion (wisoky-hills) in combination with the Top Level Domain (name) of the URL, into an IP address such as 39.29.178.34. Additionally, every web request from your computer and browser includes its type, for example:
Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
Understanding the Significance of Default Gateways
Typically, your default gateway is an automatically allocated address through DHCP. It might be a default gateway like 192.168.101.130 (although they generally end in .1 or .254, depending on the scope size), and it is the point to which your computer directs all of its traffic for routing. For a comprehensive guide on IPv6 connectivity troubleshooting, refer to our detailed discussion on how-to-fix-ipv6-connectivity/. You can also verify this on Mac or Linux systems 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 192.168.101.130 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 fe80:4874:6689:906a:49ba%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): {110.164.39.225, 142.103.247.25}
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 5d:0a:dc:f3:86: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 2f:07:1f:3d:f8:86
}
Resolve Issues with Wired or Wireless Connectivity
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.
Steps for Troubleshooting on Apple macOS / OSX
Regardless of whether you are using OSX/macOS versions such as 10.12.8, 11.3.3, or 12.2.4, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes valuable, particularly for teams that are adopting remote work and the Work From Anywhere (WFA) approach.
Utilizing Built-in Scripts for Assistance
A 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 the information is only relevant at a specific point in time 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 &. If you prefer to run it interactively, you can use the command sudo /usr/bin/sysdiagnose, which will give 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. However, be aware that the file sizes are approximately 300MB.
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