How Can I Fix MacOS No-access
Understanding Internet Address Formats
When using the Internet, you are assigned a unique numerical address, such as 163.207.111.240 for IPv4 or 2000:ad09:fb2c:ab71:6617:1bc5:8241:4d8d for IPv6. You can verify this information at https://test-ipv6.com/. However, explaining these addresses, or even MAC addresses like eb:cc:47:9e:19:88, to individuals who are not familiar with technology can be prone to errors and become complex. Furthermore, this method does not provide historical data, particularly when troubleshooting previous issues.
Navigating the World Wide Web
To access a website such as https://okon-tremblay.org, your device first consults a DNS server to convert the host section (okon-tremblay) in combination with the URL’s Top Level Domain (org) into an IP address, such as 91.246.244.172. For each web request, your computer and browser also transmit its specifications, for example: Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
Significance of Default Gateways
The default gateway is typically an automatically assigned address through DHCP. Commonly, a default gateway appears as 172.22.176.36 (usually ending in .1 or .254 based on the scope size). This is the location where your computer forwards all its traffic for further routing. For IPv6, detailed instructions can be found at how-to-fix-ipv6-connectivity/ or you can perform a check on Mac or Linux 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 172.22.176.36 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 fe80:1de0:5414:7a30:f22d%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): {226.251.89.111, 249.124.93.27}
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 eb:cc:47:9e:19:88
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 45:59:48:de:3f:e9
}
Diagnosing and Resolving Connection Issues
When it comes to transferring data through your router, you may encounter issues with either a wired or wireless (Wi-Fi) connection at the physical and data layer.
Strategies for Apple macOS / OSX Users
Regardless of whether you are using OSX or macOS, such as versions 10.13.9, 11.1.4, or 12.2.8, there are various troubleshooting tools available. However, these manual methods and scripts may not provide a comprehensive overview of correlated values over time, which is essential for remote troubleshooting. This is particularly important for teams that have adopted a remote work or Work From Anywhere (WFA) approach.
Leveraging Automated Built-in Features
One of the useful utilities on macOS/OSX is the sudo wdutil info, which can display current wireless settings in the command-line interface and generate specific logs for troubleshooting purposes. Furthermore, the sysdiagnose tool offers a more comprehensive set of logs, although many of them are only relevant to wireless connectivity, similar to wdutil.
To run sysdiagnose in the background and create logs in /var/tmp/<blah>.tar.gz, you can enter the command sudo nohup /usr/bin/sysdiagnose -u &. For an interactive approach, you can opt to run sudo /usr/bin/sysdiagnose, but be mindful of the sizable file sizes of around 300MB.
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