How To DiagnOSe OSX No-access
Demystifying Internet Addressing
When using the Internet, you may be assigned a Public IPv4 address such as 1.63.61.134 or an IPv6 address like 2000:2763:c381:c0f5:9985:7f5b:eda9:dc38. Verification of this information can be done at https://test-ipv6.com/. However, communicating these addresses to non-technical individuals or even mentioning MAC addresses like 8a:ed:e4:be:f9:3b can be challenging and prone to errors. This approach also lacks historical data, especially when dealing with previous issues.
Navigating the World Wide Web
Accessing a webpage such as https://wilderman-steuber.info involves initially reaching a DNS server to convert the host part (wilderman-steuber) and the Top Level Domain (info) of the URL into an IP address like 70.139.221.228. Every web request from your computer and browser contains its type, for instance:
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
The default gateway is typically an automatically assigned address through DHCP. You are given a default gateway like 172.26.187.90 (normally ending in .1 or .254 based on the scope size), which is where your computer forwards all its traffic to be routed further. For IPv6, a detailed explanation is available at how-to-fix-ipv6-connectivity/. Verification on Mac or Linux can be done with:
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 172.26.187.90 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:a216:5a12:6c33:23b1%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): {16.187.37.166, 42.135.146.34}
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 8a:ed:e4:be:f9:3b
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 d8:de:de:03:c7:37
}
Resolve Issues with Wired and Wireless Connections
When dealing with the physical and data layer, you have the option to use either a wired or wireless (Wi-Fi) medium to transmit data to your router.
Methods for Apple macOS / OSX Troubleshooting
Regardless of whether you are using OSX/macOS versions such as 10.14.5, 11.4.4, or 12.3.5, there are various troubleshooting tools available. However, manual actions and scripts do not provide a set of interconnected values over a specific period of time. This is where automated remote troubleshooting becomes essential, especially for teams that are transitioning towards remote work and Work From Anywhere (WFA) setups.
Utilizing Built-in Scripts for Assistance
A valuable tool on OSX/macOS is the sudo wdutil info command, which provides a detailed report of the current wireless settings through the command line interface and can also be configured to generate specific logs for troubleshooting purposes. Additionally, the sysdiagnose tool offers a more comprehensive approach to generating a wide range of logs, although most of the information is only relevant at a specific point in time, similar to the wdutil tool.
By running the command sudo nohup /usr/bin/sysdiagnose -u & in the background, the tool will write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (even though there is minimal interaction), you can execute the commandsudo /usr/bin/sysdiagnose, which will prompt a privacy warning. When not run in the background, it should open Finder in the appropriate location, or you can manually navigate to /var/tmp or use Finder along with Cmd+Shift+G to specify the path. However, be mindful of the file sizes, which can be around 300MB more or less.
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