DiagnOSe MacOS No-access

Explanation of Internet Addressing

When using the Internet, you are assigned with a Public IPv4 address, represented as 153.134.23.154, or an IPv6 address, such as 2000:3751:f206:e37e:8341:e60:e13f:7a86. A quick way to check this is through https://test-ipv6.com/. However, relaying these addresses, or even MAC addresses like 74:76:0e:6c:98:cd to those who are not as tech-savvy can lead to errors and become complex. Moreover, it does not provide any historical data.

The Process of Accessing the Web and Domain Lookups

When visiting a website like https://keeling.org, your first step is to access a DNS server that translates the host portion (keeling) and the Top Level Domain (org) of the URL into an IP address, for example 162.116.19.230. All web requests from your computer and browser include its type, such as
Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16.

The Significance of Default Gateways

The default gateway is typically an automatically assigned address via DHCP, usually ending in .1 or .254 depending on the scope size, and where your computer sends all its traffic to be routed onwards. For IPv6, detailed information about fixing connectivity can be found at how-to-fix-ipv6-connectivity/. On Mac or Linux, this can be verified with the following command:

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  192.0.0.70    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:b042:7f38:6231:d384%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): {42.32.242.22, 240.119.115.92}
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 74:76:0e:6c:98:cd
  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 9e:02:9b:9b:39:f1
}

Resolving Connectivity Issues for Wired or Wireless Networks

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

Troubleshooting Methods for Apple macOS / OSX

Regardless of the version of OSX/macOS you are using, whether it’s 10.13.8, 11.5.9, or 12.1.2, there exists a variety of troubleshooting tools. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes valuable, especially for teams that are embracing remote work and Work From Anywhere (WFA).

Utilizing Built-in Scripts and Commands

One incredibly useful tool on OSX/macOS is the sudo wdutil info, which provides a dump of the 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 point-in-time related to wireless, similar to wdutil.

To run it 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 (although there is minimal interaction), use the command
sudo /usr/bin/sysdiagnose, which will generate 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. Keep in mind that the file sizes are approximately 300MB.

Helpful Videos

Video	Title	Channel
	Mac Activity Monitor - How to Troubleshoot Your Mac	Hands-On Mac
	On the Road to Big Sur 2 - Compatibility	Hands-On Mac
	Spotlight on Spotlight - Hands-On Mac 7	Hands-On Mac
	Secret Mac Boot Commands - Mac Boot Key Combinations	Hands-On Mac
	macOS Big Sur - What's New in Apple macOS 11	Hands-On Mac

Table 1.0 - Video Help