How To Check Mac No-access
The Functioning of Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, for example, 17.50.249.101, or an IPv6 address, such as 2000:c1ba:6582:18ad:ab0f:1aa:f962:1ab8. You can verify this using https://test-ipv6.com/. However, when trying to communicate these addresses or refer to MAC addresses like 92:ba:33:db:3d:cd, it can quickly become complicated and prone to errors. Furthermore, it does not provide any historical data, particularly when dealing with past issues.
Navigating the World Wide Web
When attempting to access a web page, such as https://lowe-macgyver.io, the initial step involves contacting a DNS server to convert the host portion (lowe-macgyver) combined with the Top Level Domain (io) of the URL to an IP address, like 149.65.148.169. Your computer and browser send their type with all web requests, for example: Mozilla/5.0 (Windows; U; Win 9x 4.90; SG; rv:1.9.2.4) Gecko/20101104 Netscape/9.1.0285
Understanding the Significance of Default Gateways
Your default gateway is typically an automatically configured address via DHCP. You receive a default gateway, such as 172.30.107.182 (although they normally end in .1 or .254, depending on the scope size), and this is where your computer directs all of its traffic to be routed onwards. For IPv6, you can find detailed instructions on how-to-fix-ipv6-connectivity/, but you can also check on Mac or Linux 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 172.30.107.182 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 fe80:6d81:dd04:9e77:81b7%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): {232.189.159.154, 36.236.136.128}
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 92:ba:33:db:3d:cd
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 20:4a:2f:7c:f8:a7
}
Resolve Issues with Wired or Wireless Connection
When it comes to transmitting data to your router, you might be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
How to Address Problems on Apple macOS / OSX
Whether you are running macOS or OSX version 10.11.9, 11.4.8, or 12.1.2, there are several troubleshooting tools available. However, manual actions and scripts do not provide a consistent set of correlated values over time. This is where automated remote troubleshooting proves to be beneficial, especially for teams that have embraced remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
A useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of the current wireless settings in the CLI. It can also be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool offers a comprehensive set of logs, although much of it is only relevant to wireless settings at a specific point in time, similar to wdutil.
To run the sysdiagnose tool in the background and generate logs in /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, which will prompt a privacy warning and open Finder in the correct location. Be mindful of the file sizes, which are approximately 300MB.
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