How Can I Understand MacOS No-access
Understanding the Basics of Internet Addressing
When using the Internet, you are assigned with a Public IPv4 address such as 220.8.254.75 or an IPv6 address like 2000:d93f:bb4f:1afb:4ecc:3c3:8e57:30d. This can be verified at https://test-ipv6.com/. However, communicating these addresses, or even mentioning MAC addresses like 29:f1:cd:08:4d:cd, can be prone to errors and become complex, especially for individuals with limited technical knowledge. Additionally, it does not provide any historical data, particularly for past issues.
Navigating the World Wide Web
To access a website such as https://quitzon-parker.org, you initially contact a DNS server to convert the host portion (quitzon-parker) combined with the Top Level Domain (org) of the URL into an IP address like 178.24.253.235. Your computer and browser also 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
Understanding the Significance of Default Gateways
Your default gateway is typically an automatically configured address through DHCP. You are provided with a default gateway like 192.0.0.244 (usually ending in .1 or .254 depending on the scope size), and this is where your computer forwards all its traffic to be routed further. For IPv6, you can explore further details in our article how-to-fix-ipv6-connectivity/, or you can verify on Mac or Linux 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 192.0.0.244 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 fe80:9668:8990:b142:9e8b%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): {180.150.188.219, 122.145.227.232}
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 29:f1:cd:08:4d: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 46:26:08:c7:84:25
}
Resolve Issues with Wired and Wireless Connections
When transmitting data to your router, you might 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 running OSX/macOS version 10.12.8, 11.1.2, or 12.3.1, there are various tools available for resolving connectivity issues. However, these tools do not provide a series of correlated values over time, making it difficult to identify the root cause of the problem. This is where automated remote troubleshooting becomes invaluable, especially for teams that have adopted remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
A highly useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings in the Command Line Interface (CLI) and can be configured to generate specific logs for troubleshooting purposes. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although many of these are only relevant to a specific point in time, similar to wdutil.
To run sysdiagnose 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 prompt a privacy warning. When running it interactively, the correct location in Finder will open, or you can navigate to var/tmp, or use Finder with Cmd+Shift+G to point Finder to the path. However, be cautious of the file sizes, which can be around 300MB.
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