Understand OSX Issues
The Functioning of Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 237.170.206.51, or an IPv6 address, like 2000:f9b3:a419:876f:a74f:311:5987:4e4c. Confirmation of these addresses can be done through https://test-ipv6.com/. However, conveying or referencing these addresses, and even MAC addresses like 2e:2b:6f:05:4a:9b, can become prone to errors and complexities for individuals not well-versed in technology. Moreover, it does not provide historical data, especially when dealing with past issues.
Navigating the World Wide Web
Upon attempting to reach a webpage like https://bruen.info, the first step is accessing a DNS server to translate the host section (bruen) combined with the Top Level Domain (info) of the URL into an IP address, such as 247.49.42.56. Every web request from your computer and browser includes its type, for instance: Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
The Significance of Default Gateways
Typically, your default gateway is an automatically configured address via DHCP. It is a default gateway like 10.85.12.53 (though they typically end in .1 or .254 based on their scope size) that your computer uses to route all its traffic. A comprehensive guide on how to check on Mac or Linux for IPv6 can be found at how-to-fix-ipv6-connectivity/.
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 10.85.12.53 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 fe80:16f8:518b:8e03:4b14%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): {218.7.252.119, 139.81.252.203}
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 2e:2b:6f:05:4a:9b
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 59:98:6c:83:a3:64
}
Resolving Issues with Wired and Wireless Connections
When transmitting data to your router, you may use either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Techniques for Apple macOS / OSX
Regardless of the version of OSX/macOS you are using, whether it is 10.12.5, 11.0.5, or 12.0.5, there are various tools available for resolving issues. However, these manual actions and scripts alone do not provide a series of correlated values over time, making automated remote troubleshooting especially valuable for teams that embrace remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts for Assistance
On OSX/macOS, the sudo wdutil info tool is quite beneficial as it provides a dump to the CLI of current wireless settings, and it can also be configured to generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool offers comprehensive logging capabilities, although much of it pertains to wireless settings at a specific point in time, similar to wdutil.
To run sysdiagnose in the background and generate logs in /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. Alternatively, for an interactive (albeit minimal interaction) experience, you can run sudo /usr/bin/sysdiagnose, which will display a privacy warning. If not run in the background, the tool should open Finder in the correct location, or you can navigate to /var/tmp using Finder with Cmd+Shift+G to access the folder. Keep in mind that the file sizes are approximately 300MB.
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