How Can I Understand OSX No-access
Understanding Internet Addressing
When using the Internet, your device may be assigned a Public IPv4 address, such as 121.216.69.197, or an IPv6 address, like 2000:2203:da82:b62a:6c10:4f13:632a:5970. You can verify this information by visiting https://test-ipv6.com/. However, conveying and dealing with these complex addresses, and even MAC addresses like e5:bb:fa:d9:94:0a, can be prone to errors and become convoluted. Moreover, this method does not provide any historical data, particularly with past issues.
Navigating the World Wide Web
When attempting to access a web page, such as https://lueilwitz.info, the first step involves contacting a DNS server to convert the combination of the host portion (lueilwitz) and the Top Level Domain (info) of the URL to an IP address, like 117.198.170.253. With each web request, your computer and browser also transmit their type, as demonstrated in this example: Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
The Significance of Default Gateways
Most often, your default gateway is automatically configured through DHCP and appears as an address like 10.132.58.114 (although it typically ends in .1 or .254 based on the scope size). This is the location where your computer directs all its traffic for onward routing. For an in-depth explanation on dealing with IPv6, visit how-to-fix-ipv6-connectivity/. Additionally, on Mac or Linux systems, you can verify this information.
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 10.132.58.114 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 fe80:400b:6571:b26e:1882%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): {167.84.61.159, 213.73.10.15}
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 e5:bb:fa:d9:94:0a
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 cd:e5:c5:86:40:91
}
Resolve Issues with Wired and Wireless Connections
When transmitting data to your router, you may utilize either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting on Apple’s macOS / OSX Operating System
Regardless of the version of OSX/macOS you are using, whether it’s 10.15.2, 11.3.8, or 12.2.3, there are various tools available for resolving issues. However, manual actions and scripts do not provide a comprehensive set of correlated values over time. Automated remote troubleshooting becomes crucial, especially for teams that embrace remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts for Assistance
A helpful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the 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 most are only point-in-time data related to wireless, similar to wdutil.
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, use the command sudo /usr/bin/sysdiagnose with caution regarding file sizes of approximately 300MB. Afterward, navigate to /var/tmp in Finder or use the Cmd+Shift+G shortcut in Finder to locate the files.
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