Understand Mac No-access
Explanation of Internet Addressing
When using the Internet, individuals may possess a Public IPv4 address such as 111.46.141.113 or an IPv6 address such as 2000:45f6:1cb8:1770:b51d:efe3:52af:2fe7. These addresses can be verified using https://test-ipv6.com/. Conveying these addresses, or even mentioning MAC addresses like 36:0f:4d:c3:fc:9d, can be error-prone and complicated, especially for those who are not technologically inclined. Additionally, historical data is not provided, which can be important for understanding past issues.
Navigating the World Wide Web
When attempting to access a website, such as https://walsh-hickle.biz, the first step is to contact a DNS server. This server translates the host portion (walsh-hickle) in conjunction with the Top Level Domain (biz) of the URL, into an IP address like 67.19.127.171. Furthermore, the computer and browser include their type when making web requests, for example:
Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
Understanding the Significance of Default Gateways
The default gateway is typically an address that is automatically configured via DHCP. A default gateway, such as 172.22.32.43 (usually ending in .1 or .254 based on the scope size), is where a computer sends all of its traffic to be routed forward. For IPv6, a comprehensive explanation can be found at how-to-fix-ipv6-connectivity/, and individuals utilizing Mac or Linux operating systems can verify this using:
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 172.22.32.43 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:b85b:95:71a4:f0b4%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): {136.43.151.104, 184.46.42.217}
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 36:0f:4d:c3:fc:9d
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 65:04:6e:0e:b9:1b
}
How to Address Issues with Wired and Wireless Connectivity
When it comes to transmitting data to your router, you may be utilizing a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of whether your operating system is OSX/macOS version 10.12.3, 11.6.4, or 12.0.9, there are various troubleshooting tools available. However, these tools do not provide a series of correlated values over time, and this is where automated remote troubleshooting becomes especially valuable, especially for remote work and Work From Anywhere (WFA) teams.
Useful Built-in Scripts
One tool that can be very helpful on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI and can also be configured to generate specific troubleshooting logs. Additionally, the sysdiagnose tool can be used to generate a wide range of logs related to wireless issues, similar to wdutil.
To run it 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, but be cautious of the large file sizes of about 300MB.
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