Understand Apple Connectivity

Understanding Internet Addressing

When using the Internet, you are assigned a Public IPv4 address, such as 154.216.144.51 or an IPv6 address like 2000:1b9f:7b01:b73e:f086:8f75:225a:c20c. You can verify this on https://test-ipv6.com/. However, for individuals who are not well-versed in technology, communicating these addresses, or even recognizing MAC addresses like c9:f1:c0:db:09:b5, can be prone to errors and become complex. Moreover, this method does not provide any historical data, especially pertaining to past issues.

Process of Accessing the Internet

When attempting to access a website, such as https://pfeffer-dickinson.com, the first step involves contacting a DNS server to translate the specific host portion (pfeffer-dickinson) along with the Top Level Domain (.com) of the URL into an IP address, like 37.160.253.84. Your computer and browser include its type in 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

Typically, your default gateway is an address that is automatically configured via DHCP. This gateway can be something like 172.21.249.120 (although they usually end in .1 or .254 depending on the scope size), and it is the destination where your computer sends all its traffic to be routed onwards. For IPv6, detailed instructions can be found in our blog post how-to-fix-ipv6-connectivity/, but you can verify this on Mac or Linux by 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  172.21.249.120    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   fe80:3663:3d04:6654:8ea9%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): {203.27.209.56, 167.161.164.96}
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 c9:f1:c0:db:09:b5
  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 68:28:71:8f:e0:c4
}

Resolve Issues with Wired or Wireless Connections

When it comes to transmitting data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.

Troubleshooting on Apple’s macOS / OSX Systems

Regardless of whether you are running OSX/macOS version 10.11.9, 11.1.8, or 12.3.4, there are numerous tools available for troubleshooting. However, these manual actions and scripts do not provide a comprehensive set of correlated values over time. This is where automated remote troubleshooting becomes invaluable, particularly for teams that are embracing remote work and Work From Anywhere (WFA).

Effective Built-in Scripts

One incredibly useful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI and can also be configured to generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool offers a more comprehensive option for generating a wide range of logs (although many of them are point-in-time related to wireless, similar to wdutil).

Running sudo nohup /usr/bin/sysdiagnose -u & will execute it in the background, writing logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (although there isn’t much interaction), you can use
sudo /usr/bin/sysdiagnose, which will prompt 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. Be mindful of the file sizes, which are approximately 300MB.

Possibly Helpful Videos

Video	Title	Channel
	Mac Activity Monitor - How to Troubleshoot Your Mac	Hands-On Mac
	Secret Mac Boot Commands - Mac Boot Key Combinations	Hands-On Mac
	On the Road to Big Sur 2 - Compatibility	Hands-On Mac
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Table 1.0 - Video Help