How Do You Understand OSX No-access
Demystifying Internet Addressing
When you use the Internet, you are assigned a Public IPv4 address, such as 244.165.139.13, or an IPv6 address like 2000:c650:8503:48a5:f47:c9b3:50d:b358. You can verify this by visiting https://test-ipv6.com/. However, for those who are not technically inclined, communicating these addresses, or even identifying MAC addresses like f6:6b:ce:28:f0:f5, can be error-prone and complex. Furthermore, this method does not provide any historical data, especially for past issues.
Navigating the World Wide Web
When you access a website like https://weber.net, you first contact a DNS server to translate the host portion (weber) combined with the Top Level Domain (net) of the URL into an IP address, such as 119.149.53.132. Your computer and browser also include their types in all web requests, for example:
<br>Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
Understanding the Significance of Default Gateways
Your default gateway is usually an automatically configured address obtained via DHCP. It may be a default gateway like 10.224.90.40 (although they typically end in .1 or .254, depending on the scope size), and it is the location where your computer sends all its traffic to be routed onwards. For IPv6, you can find more information in our in-depth guide on how-to-fix-ipv6-connectivity/, or you can check on Mac or Linux with the following commands:
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 10.224.90.40 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 fe80:510e:4f9d:7557:ec64%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): {14.167.136.198, 13.156.156.13}
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 f6:6b:ce:28:f0:f5
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 8f:e1:9c:02:1b:42
}
Fixing Connectivity Issues in Wired and Wireless Networks
When transmitting data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Resolving Problems on Apple MacOS / OSX
Regardless of the version of OSX/macOS you have - whether it’s 10.12.4, 11.0.1, or 12.0.4 - there are various troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes essential, particularly for teams that are transitioning towards remote work and embracing Work From Anywhere (WFA) practices.
Utilizing Pre-Installed Scripts for Assistance
A highly useful tool 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 logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it pertains to wireless and is only relevant at a specific point in time, similar to wdutil.
To run sysdiagnose in the background and generate logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, use the command sudo /usr/bin/sysdiagnose, which will display a privacy warning. Not running it in the background will 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 can be around 300MB.
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