How To Check MacOS No-access
Understanding Internet Addressing
When using the Internet, your device is assigned a unique public IPv4 address, such as 27.154.128.108, or an IPv6 address, like 2000:944d:55b0:27e1:a8df:c479:364d:6ffa. This information can be verified using a website like https://test-ipv6.com/. However, conveying these addresses to individuals who are not tech-savvy, or even mentioning MAC addresses such as 95:ff:4b:18:2f:7e, can be prone to error and become complex, particularly when attempting to communicate historical data from previous incidents.
Navigating the Web
When trying to access a website like https://aufderhar.org, the initial step involves consulting a DNS server to convert the host portion (aufderhar) along with the Top Level Domain (org) of the URL into an IP address, such as 222.142.36.77. Additionally, every web request sent from your computer and browser contains its type, for example: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36
The Significance of Default Gateways
By default, your gateway is an address automatically configured via DHCP. This gateway typically appears as an address like 192.0.0.73 (often ending in .1 or .254 depending on the scope size), and it’s the point where your computer sends all of its traffic to be routed onward. For IPv6, an in-depth explanation is available at how-to-fix-ipv6-connectivity/, and you can check it 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 192.0.0.73 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:c54c:cc5c:6604:3e9b%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): {223.118.217.205, 50.81.249.253}
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 95:ff:4b:18:2f:7e
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 a0:51:a3:5c:67:ea
}
Resolving Issues with Wired and Wireless Connections
When it comes to transferring data to your router, you could be utilizing a wired or wireless (Wi-Fi) medium at the physical and data layer.
Effective Solutions for Apple macOS / OSX Users
Regardless of whether you are using OSX/macOS versions such as 10.12.4, 11.2.4, or 12.2.9, there are various tools available for troubleshooting. Unfortunately, the manual remedies and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams that are adopting remote work and Work From Anywhere (WFA).
Practical Built-in Tools for Assistance
One extremely useful tool on OSX/macOS is sudo wdutil info, which provides a dump of the current wireless settings to the CLI, and can also be configured to produce specific logs for troubleshooting. Moreover, the sysdiagnose tool can be utilized to generate a multitude of logs, although much of it is only relevant to the wireless settings, similar to wdutil.
By running sudo nohup /usr/bin/sysdiagnose -u &, you can execute it in the background and it will write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (although there isn’t much interaction), you can use the command sudo /usr/bin/sysdiagnose and it will display a privacy warning. When not run in the background, it should open Finder in the appropriate location, or you can navigate to /var/tmp or use Finder with Cmd+Shift+G to direct Finder to the path. Just be cautious of the file sizes, which are approximately 300MB more or less.
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