DiagnOSe Apple No-access

Understanding IP Addressing and Communication

When using the Internet, you are assigned either a Public IPv4 address or an IPv6 address. These addresses can be verified from a site like https://test-ipv6.com/. However, conveying these addresses, or even MAC addresses, to individuals without technical knowledge can quickly become complicated and prone to errors. Moreover, these addresses do not provide any historical data, particularly for past issues.

Navigating the World Wide Web

Accessing a website like https://vonrueden-marks.net involves initially contacting a DNS server to convert the URL’s host portion and Top Level Domain to an IP address. Your computer and browser sends its type with web requests, such as: Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)

The Significance of Default Gateways

Typically configured automatically via DHCP, your default gateway, such as 192.0.0.51, is where your computer directs all its traffic to be routed onwards. For IPv6 connectivity solutions on Mac or Linux, refer to how-to-fix-ipv6-connectivity.

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  192.0.0.51    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   fe80:9937:e1a8:8be5:ccd%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): {183.224.202.171, 65.237.239.29}
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 be:ae:ed:ee:53:10
  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 c4:a2:f9:86:5c:fa
}

Resolve Issues with Wired or 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 Tips for Apple macOS / OSX

Regardless of whether you are using OSX/macOS “10.14.2”, “11.4.2”, or “12.3.6”, there are various tools available for troubleshooting. However, manual actions and scripts do not provide a set 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).

Useful Built-in Tools for Troubleshooting

One useful 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 most are only relevant to wireless at a specific point in time, similar to wdutil.

To run the sysdiagnose tool in the background, use the command “sudo nohup /usr/bin/sysdiagnose -u &”, which will write logs to “/var/tmp/.tar.gz”. Alternatively, for an interactive experience, you can run “sudo /usr/bin/sysdiagnose” which will display 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 or through the path. Keep in mind that the file sizes are approximately 300MB.

Possibly Helpful Videos

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	Mac Activity Monitor - How to Troubleshoot Your Mac	Hands-On Mac
	macOS Big Sur - What's New in Apple macOS 11	Hands-On Mac
	Spotlight on Spotlight - Hands-On Mac 7	Hands-On Mac
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Table 1.0 - Video Help