How Can I Troubleshoot MacOS No-access
Navigating Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 208.78.229.66, or an IPv6 address, like 2000:d271:575f:99e:f0f7:6494:4f04:3585. A convenient way to check this is through https://test-ipv6.com/. However, explaining and relaying these addresses to those less knowledgeable in technology, and even mentioning MAC addresses like 3c:cd:58:55:f1:1e, can lead to errors and become complicated quickly. Furthermore, this method does not provide any historical data, especially when referring to previous problems.
Reaching the World Wide Web
When attempting to access a webpage, such as https://turcotte.biz, you first connect to a DNS server to convert the host portion (turcotte) combined with the Top Level Domain (biz) of the URL into an IP address, like 21.233.173.12. Moreover, your computer and browser transmit their type with all web requests, for example: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 address assigned automatically via DHCP. It can be a default gateway like 192.168.103.138, although they typically end in .1 or .254 depending on the scope size. This is the point where your computer directs all its traffic to be routed onwards. For IPv6, a comprehensive guide is available at how-to-fix-ipv6-connectivity/, or you can perform checks 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 192.168.103.138 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:dea6:9bec:51ef:f2e%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): {59.71.224.165, 159.130.233.43}
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 3c:cd:58:55:f1:1e
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 00:bd:4a:8d:18:ac
}
Resolving Issues with Wired and Wireless Connections
When transmitting data to your router, you may utilize either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of the version of OSX/macOS you are using, whether it’s 10.13.4, 11.3.6, or 12.0.1, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes beneficial, particularly for teams that are embracing remote work and Work From Anywhere (WFA).
Pre-Installed Scripts for Assistance
A highly useful tool on OSX/macOS is the sudo wdutil info, which provides a dump of the current wireless related settings to the CLI, and can also be configured to generate specific troubleshooting logs. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant to wireless issues, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & will execute the tool in the background and write logs to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively (although there isn’t much interaction), you can use sudo /usr/bin/sysdiagnose, which will prompt a privacy warning. When 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 locate the path. However, be cautious of the file sizes, which are approximately 300MB.
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