How Can I Troubleshoot Mac Connectivity
Demystifying Internet Addressing
When using the Internet, you are assigned a Public IPv4 address such as 164.202.185.34 or an IPv6 address like 2000:5423:339:5b33:8670:937e:5c7d:352f. You can verify this information at https://test-ipv6.com/. However, conveying these addresses, or MAC addresses like 1d:1e:ba:f6:0a:75, to those without technical knowledge can be prone to errors and can become complex. Moreover, this method does not provide any historical data, especially regarding past issues.
Understanding Web Access
When accessing a web page, such as https://bode-rodriguez.io, the first step is to consult a DNS server to translate the URL’s host portion (bode-rodriguez) and Top Level Domain (io) into an IP address like 233.215.237.237. The computer and browser specify their type with every web request, for example: Mozilla/5.0 (Windows; U; Win 9x 4.90; SG; rv:1.9.2.4) Gecko/20101104 Netscape/9.1.0285
Significance of Default Gateways
By default, your gateway is typically assigned through DHCP and appears as an address like 192.0.0.110 (often ending in .1 or .254 depending on the scope size). This is where your computer sends all its traffic for further routing. For IPv6, a comprehensive guide is available at how-to-fix-ipv6-connectivity/. You can also verify this 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 192.0.0.110 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 fe80:2766:f0a4:d59e:5a55%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): {147.191.200.70, 193.247.97.156}
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 1d:1e:ba:f6:0a:75
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 0e:03:e7:c5:53:54
}
Fixing Connection Issues with Wired or Wireless Networks
When it comes to sending data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of whether you are using OSX/macOS versions such as 10.12.6, 11.2.8, or 12.3.5, there are various tools available to help with troubleshooting. However, these tools do not provide a series of correlated values over time, which is where automated remote troubleshooting becomes particularly useful, especially for teams that work remotely and support a Work From Anywhere (WFA) approach.
Using Built-in Scripts for Assistance
One useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can also generate specific logs for troubleshooting. Another tool, the sysdiagnose command, can generate a wide range of logs, although many of them are only relevant to wireless issues, similar to wdutil.
To run the sysdiagnose command in the background and write logs to /var/tmp/<blah>.tar.gz, you can use the sudo nohup /usr/bin/sysdiagnose -u & command. If you prefer to run it interactively, you can use the sudo /usr/bin/sysdiagnose command, but be aware of the large file sizes, approximately 300MB or more.
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