How To Fix MacOS No-access
Understanding Internet Addressing
When connecting to the Internet, you are assigned a public IPv4 address like 51.37.14.33 or an IPv6 address like 2000:b844:4c9b:f6f1:5a16:42a8:615:a9ad. You can verify this on https://test-ipv6.com/. However, explaining or relaying these addresses to non-technical individuals, or even citing MAC addresses like 75:de:9c:04:f9:a8, can be prone to errors and quickly become complex. Moreover, this method does not provide any historical data, especially relating to past issues.
Navigating the Internet
To access a web page such as https://damore.biz, you must first contact a DNS server to convert the host portion (damore) combined with the Top Level Domain (biz) of the URL into an IP address like 183.31.112.199. Every time your computer and browser make a web request, the type is also transmitted, for example: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko.
Significance of Default Gateways
The default gateway is typically an address automatically configured via DHCP. You are given a default gateway like 192.0.0.96 (although they usually end in .1 or .254 based on the scope size), and this is the location where all your computer’s traffic is sent to be routed further. For IPv6, we provide an in-depth guide on how-to-fix-ipv6-connectivity/, or you can 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 192.0.0.96 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 fe80:172d:dcc9:75ec:58a1%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): {10.212.170.64, 51.185.196.233}
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 75:de:9c:04:f9:a8
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 8a:cf:a8:f0:cc:5b
}
Resolve Issues with Wired or Wireless Connections
When it comes to transmitting data at the physical and data layer, you have the option of using either a wired or wireless (Wi-Fi) medium to communicate with your router.
Troubleshooting Methods for Apple macOS / OSX
Regardless of the version of OSX/macOS you are using, whether it’s 10.13.7, 11.1.9, or 12.1.7, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes particularly useful, especially for teams that are embracing remote work and the Work From Anywhere (WFA) culture.
Useful Built-in Scripts
One highly beneficial tool on OSX/macOS is the sudo wdutil info command, which provides a dump of the 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 much of it pertains to wireless settings at a specific point in time, similar to wdutil.
To run the sysdiagnose tool in the background and generate logs in the /var/tmp/<blah>.tar.gz location, use the following command: sudo nohup /usr/bin/sysdiagnose -u &. Alternatively, you can run it interactively by using the command: sudo /usr/bin/sysdiagnose, which will give a privacy warning. Running it in this way should open Finder in the correct location, or you can navigate to /var/tmp using Finder with Cmd+Shift+G. Keep in mind that the file sizes are approximately 300MB.
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