How Do You Troubleshoot MacOS No-access
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 201.44.67.188, or an IPv6 address, like 2000:63be:c145:3557:c9c9:5f1:e3d9:dca5. You can verify this information by visiting https://test-ipv6.com/. However, for those who are not well-versed in technology, communicating these addresses, as well as MAC addresses like ec:06:ab:5e:f1:74, can be prone to errors and can become complicated very quickly. Moreover, this method does not provide any historical data, particularly when dealing with past issues.
Navigating the World Wide Web
When accessing a website such as https://boyle.io, your first step involves contacting a DNS server to translate the host portion (boyle) together with the Top Level Domain (io) of the URL into an IP address, such as 47.70.188.95. Your computer and browser include its type in all web requests, for example: Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)
Understanding the Significance of Default Gateways
Your default gateway is typically an automatically configured address via DHCP. You receive a default gateway, such as 192.0.0.212 (although they typically end in .1 or .254 depending on the scope size), and this is where your computer sends all its traffic to be routed onwards. For IPv6, you can refer to our in-depth guide on how-to-fix-ipv6-connectivity/ or you can verify on Mac or Linux using the following command:
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 192.0.0.212 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 fe80:3dfd:4fd6:2847:14b3%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): {223.147.188.143, 169.89.90.251}
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 ec:06:ab:5e:f1:74
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 d9:63:89:f7:e6:f4
}
Resolve Issues with Wired or Wireless Connection
When it comes to transmitting data to your router, you might be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting on Apple macOS / OSX
No matter which version of OSX/macOS you’re running, whether it’s 10.12.6, 11.0.3, or 12.2.8, there are various tools available for resolving issues. 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 embracing remote work and Work From Anywhere (WFA).
Useful Built-in Tools
A highly beneficial tool on OSX/macOS is the sudo wdutil info, which provides a dump of current wireless-related settings on the CLI, and can also be configured to generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant to wireless settings, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (although there is not much interaction), you can use sudo /usr/bin/sysdiagnose, which will prompt a privacy warning. If not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp or use Finder with Cmd+Shift+G to point Finder to the path. Just be aware of file sizes, which are approximately 300MB.
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