How Can I Troubleshoot OSX Issues

Understanding Internet Addressing

When it comes to the Internet, you might have a Public IPv4 address, such as 13.238.189.206, or an IPv6 address, such as 2000:c77c:db2b:a907:9e9a:6650:984d:6cdf. Verification of this information can be done at https://test-ipv6.com/. However, attempting to communicate these addresses to individuals who are not technologically savvy can be error-prone and complex, particularly when dealing with MAC addresses like 5b:59:c5:be:60:61. Moreover, this method does not provide historical data, especially from previous incidents.

Navigating the World Wide Web

Visiting a webpage such as https://stoltenberg.co involves initially accessing a DNS server to translate the host section (stoltenberg) combined with the URL’s Top Level Domain (co) to an IP address like 173.241.134.113. Furthermore, your computer and browser transmit their type with every web request, such as:
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A

Recognizing the Significance of Default Gateways

Your default gateway is typically an automatically assigned address via DHCP. You will receive a default gateway, such as 172.19.237.18 (typically ending in .1 or .254 based on the scope size), which is where your computer sends all traffic for routing. For a more detailed overview on IPv6, visit how-to-fix-ipv6-connectivity/, and on Mac or Linux, you can check 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  172.19.237.18    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:f2d0:60e9:9544:e324%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): {137.128.155.244, 7.108.222.151}
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 5b:59:c5:be:60:61
  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 a2:da:a0:73:db:6e
}

Resolving Connectivity Issues for Wired and Wireless Networks

When it comes to transmitting data, whether through a wired or wireless (Wi-Fi) connection, you are operating at the physical and data layer, ultimately sending the data to your router.

Troubleshooting Strategies for Apple macOS / OSX Users

Regardless of whether you are using OSX or macOS, whether it’s version 10.13.3, 11.6.9, or 12.3.8, there are various tools available for troubleshooting. However, these manual procedures and scripts do not provide a set of interconnected values over time. This is where remote automated troubleshooting becomes particularly valuable, especially for teams that have embraced remote work and the Work From Anywhere (WFA) model.

Utilizing Built-in Scripts for Assistance

One incredibly useful tool in OSX/macOS is the sudo wdutil info command, which provides a dump of the current wireless settings to the CLI, and it can be configured to generate specific logs for troubleshooting purposes. Furthermore, the sysdiagnose tool can be used to generate a wide array of logs, although most of it is related to wireless settings and is only a snapshot in time, similar to wdutil.

Running sudo nohup /usr/bin/sysdiagnose -u & in the background will generate logs in /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (even though there isn’t much interaction), you can use the command
sudo /usr/bin/sysdiagnose and it will display a privacy warning. If it’s not run in the background, it should open Finder in the right location, or you can navigate to /var/tmp or use Finder with Cmd+Shift+G to direct Finder to the path. Just be mindful of the file sizes, which are around 300MB give or take.

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Table 1.0 - Video Help