How Do You Troubleshoot OSX No-access
The Functioning of Internet Address Allocation
When using the Internet, individuals may acquire a Public IPv4 address such as 171.78.42.230 or an IPv6 address such as 2000:f559:22f2:4ff6:2205:9a06:380b:9b0c. The validity of these addresses can be verified at https://test-ipv6.com/. However, for those who are not technologically inclined, attempting to relay these addresses or even cite MAC addresses, like fa:16:9f:dd:94:6c, can lead to errors and a rapid increase in complexity. Moreover, this method fails to provide any historical data, particularly in relation to prior issues.
Navigating the World Wide Web
Accessing a website such as https://wilkinson.net involves an initial interaction with a DNS server, which translates the host portion (wilkinson) in conjunction with the Top Level Domain (net) of the URL into an IP address, for example, 105.254.224.25. During all web requests, your computer and browser transmit their type, as evidenced by the string: Mozilla/5.0 (Windows; U; Win 9x 4.90; SG; rv:1.9.2.4) Gecko/20101104 Netscape/9.1.0285
The Significance of Default Gateways
Typically, your default gateway is automatically configured via DHCP and results in an address like 192.168.118.13 (although they generally end in .1 or .254 based on the scope size). This gateway serves as the routing destination for all the traffic emanating from your computer. In the case of IPv6, a comprehensive guide on the topic can be found at how-to-fix-ipv6-connectivity/. Additionally, the gateway can be verified 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 192.168.118.13 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:f6a2:94a0:3878:d59d%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): {86.232.9.32, 145.180.154.116}
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 fa:16:9f:dd:94:6c
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 2b:1b:45:43:a9:2e
}
How to Troubleshoot Wired and Wireless Connections
When it comes to transmitting data to your router, you may be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Solutions for macOS / OSX Issues
Regardless of whether you are using OSX or macOS versions such as 10.13.2, 11.0.7, or 12.3.6, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a consistent set of correlated values over time. This is where automated remote troubleshooting becomes essential, especially for teams that prefer remote work and Work From Anywhere (WFA).
Useful Built-in Tools
On OSX/macOS, the sudo wdutil info command is a useful tool that provides a dump of current wireless settings to the command-line interface and can also generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can generate a wide range of logs related to wireless issues, similar to wdutil.
To run sysdiagnose in the background and create logs in /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. For interactive use, run sudo /usr/bin/sysdiagnose, which will issue a privacy warning, and then navigate to the correct location in Finder or use Cmd+Shift+G to locate the path. Keep in mind that the file sizes are approximately 300MB.
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