How Do You Understand OSX Issues
Understanding Internet Addressing
When using the Internet, you are assigned a unique Public IPv4 address, such as 153.145.87.32, or an IPv6 address like 2000:3d76:bb22:4b92:b99f:4597:f127:3e2. You can verify this information by visiting https://test-ipv6.com/. Communicating these addresses, including MAC addresses such as 19:5d:b4:8d:84:46, can be challenging for those who are not familiar with technical jargon and can become complex very quickly. Furthermore, this method does not provide any historical data, particularly when addressing past issues.
Navigating the World Wide Web
Accessing a website like https://larkin.org involves initially connecting to a DNS server to translate the host portion (larkin) combined with the Top Level Domain (org) of the URL to an IP address, such as 38.138.75.191. Whenever you make web requests, your computer and browser send specific information, such as `Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
The Significance of Default Gateways
Your default gateway is typically an address that is automatically configured via DHCP. This address, such as 192.0.0.63 (although they generally end in .1 or .254 depending on the scope size), is where your computer sends all of its traffic to be routed onwards. For IPv6, detailed instructions on how to check this on Mac or Linux 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 192.0.0.63 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:f08c:80a5:66b5:51c3%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): {162.200.95.250, 190.94.44.22}
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 19:5d:b4:8d:84:46
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 d4:f4:52:25:c1:c1
}
Resolve Connectivity Issues for Wired or Wireless Networks
When it comes to transferring data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Effective Solutions for Apple macOS / OSX Users
Regardless of whether you are running OSX/macOS versions such as 10.13.2, 11.5.1, or 12.3.1, there are various troubleshooting tools available. However, these manual interventions and scripts do not provide a set of correlated values over a period of time. This is where automated remote troubleshooting becomes advantageous, particularly for teams that embrace remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One particularly handy tool on OSX/macOS is the sudo wdutil info command, which provides a dump of the current wireless settings to the CLI and can also be configured to generate specific logs for troubleshooting. Moreover, the sysdiagnose tool offers a more comprehensive option for generating a wide range of logs (although much of it is only relevant to the wireless settings similar to wdutil).
Executing the command sudo nohup /usr/bin/sysdiagnose -u & will run sysdiagnose in the background and save logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (although there is minimal interaction), you can execute sudo /usr/bin/sysdiagnose and it 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 using Finder with Cmd+Shift+G. Be mindful of the file sizes, which are approximately 300MB.
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