How Can I Understand MacOS Issues
Functioning of Internet Addressing
When using the Internet, you may be assigned a Public IPv4 address such as 208.167.225.189 or an IPv6 address like 2000:ae96:3845:612d:7433:39d8:eb86:9a4a. You can verify this at https://test-ipv6.com/. However, for those who are not technically inclined, communicating these addresses, or even discussing MAC addresses like 9d:94:56:c8:1d:56, can quickly become complicated and prone to errors. Additionally, this does not provide any historical data, particularly when encountering previous issues.
Navigating the Internet
Accessing a website such as https://hamill.name involves first reaching a DNS server to convert the host portion (hamill) combined with the Top Level Domain (name) of the URL to an IP address, like 37.167.185.241. When making web requests, your computer and browser actually sends its user-agent type, such as Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts).
Significance of Default Gateways
Your default gateway is typically an automatically configured address via DHCP. A default gateway like 192.0.0.32 is assigned (although they usually end in .1 or .254 depending on the scope size), and this is where your computer sends all its traffic to be routed onwards. For IPv6, there is an in-depth guide available on how-to-fix-ipv6-connectivity/, but you can also check 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 192.0.0.32 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:c3e8:493d:f728:4058%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): {158.157.193.166, 19.227.76.94}
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 9d:94:56:c8:1d:56
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 f8:8e:a4:1a:c6:39
}
Resolve Issues with Wired or Wireless Connections
When it comes to transmitting data to your router, you may be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Solutions for Apple macOS / OSX
Regardless of the version of OSX/macOS you are running, whether it’s 10.12.8, 11.3.8, or 12.0.1, there are various tools available for resolving issues. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting shines, particularly for teams that are embracing remote work and the Work From Anywhere (WFA) concept.
Utilize Built-in Scripts
One valuable tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless related settings to the CLI, and can also be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant to wireless at a specific point in time, similar to wdutil.
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. For an interactive (although not very interactive) experience, run sudo /usr/bin/sysdiagnose and it will display 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. Keep in mind that the file sizes are approximately 300MB.
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