How Do You DiagnOSe MacOS No-access
The Functioning of Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 200.107.26.248, or an IPv6 address, like 2000:c89f:3d6f:a084:e719:bd5c:a853:3aaa. You can verify this information by visiting https://test-ipv6.com/. However, communicating these addresses, including MAC addresses like bd:55:25:1f:f6:13, can be prone to errors and become complex, especially for those who are not technologically inclined. Moreover, it fails to provide historical data, particularly from past issues.
Navigating the World Wide Web
In order to reach a website, such as https://huel-heidenreich.info, you first access a DNS server to convert the host section (huel-heidenreich) along with the URL’s Top Level Domain (info) to an IP address like 254.131.181.78. When making web requests, your computer and browser actually transmit their type, for example Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36
Understanding the Significance of Default Gateways
Your default gateway is typically an automatically configured address through DHCP. It assigns a default gateway, like 192.0.0.116 (although they usually end in .1 or .254 depending on the scope size), which is where your computer directs all its traffic to be routed. For IPv6, we have an in-depth guide on how-to-fix-ipv6-connectivity/, or you can check on Mac or Linux by:
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 192.0.0.116 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 fe80:6560:c2fa:5ba0:88ee%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): {90.178.149.163, 95.182.189.54}
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 bd:55:25:1f:f6:13
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 ea:ac:e9:17:e9:f3
}
Resolving Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you have the option of using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Effective Solutions for Apple macOS / OSX Users
Regardless of whether you are using OSX or macOS version 10.13.4, 11.3.3, or 12.0.9, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a series of correlated values over time. This is particularly where automated remote troubleshooting proves to be invaluable, especially for teams that are transitioning to remote work and embracing the concept of Work From Anywhere (WFA).
Utilizing In-Built Scripts for Troubleshooting
One extremely useful tool on OSX/macOS is the 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 purposes. Additionally, the sysdiagnose tool can be used to generate a comprehensive range of logs, although much of it is only applicable to wireless issues similar to wdutil.
To run it in the background and generate logs in /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can use sudo /usr/bin/sysdiagnose with 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 cautious of the file sizes, which can be around 300MB more or less.
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