Understand MacOS Issues
The Functioning of Internet Addressing
When it comes to the Internet, you may have a Public IPv4 address such as 171.80.184.215 or an IPv6 address like 2000:3c31:9884:b1a9:1560:f58f:248d:ef33. Verification of these addresses can be performed using https://test-ipv6.com/. However, for individuals who are not tech-savvy, communicating these addresses or even mentioning MAC addresses like 46:31:1e:7a:b4:1c can be prone to error and may become complex rapidly. Moreover, it fails to provide any historical data, especially regarding previous issues.
Navigating the World Wide Web
In order to access a web page like https://bode.net, the initial step involves accessing a DNS server to convert the host part (bode) along with the Top Level Domain (net) of the URL, to an IP address such as 118.104.23.123. Whenever any web request is made, your computer and browser actually transmit their type, for instance Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)
The Significance of Default Gateways
By and large, your default gateway is an address that is automatically configured via DHCP. This results in obtaining a default gateway like 192.0.0.76 (though they generally end in .1 or .254 depending on the scope size) and is where your computer directs all its traffic to be routed further. For a comprehensive guide on IPv6, refer to how-to-fix-ipv6-connectivity/ Alternatively, you can perform a check 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 192.0.0.76 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 fe80:5b19:7d6a:fb6d:99cb%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): {51.39.237.52, 115.32.218.157}
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 46:31:1e:7a:b4:1c
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 c9:a0:74:80:c8:6c
}
Resolving Issues with Wired and Wireless Connections
When it comes to the physical and data layer, you have the option of using either a wired or wireless (Wi-Fi) medium to transmit data to your router.
Troubleshooting Tips for Apple macOS / OSX
No matter which version of OSX/macOS you are running - whether it’s 10.14.1, 11.4.7, or 12.2.7 - there are various resources available for addressing issues. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes essential, especially for teams that have adopted remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One valuable tool on OSX/macOS is the sudo wdutil info, which offers a dump of current wireless settings to the CLI, and can also be configured to generate specific troubleshooting logs. Additionally, the sysdiagnose tool provides a comprehensive range of logs, although much of it is only point-in-time data in relation to wireless, similar to wdutil.
sudo nohup /usr/bin/sysdiagnose -u & will run it in the background and write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (although there isn’t much interaction), you can run sudo /usr/bin/sysdiagnose, which will prompt a privacy warning. When not run in the background, it should open Finder in the correct location, where you can navigate to /var/tmp, or use Finder with Cmd+Shift+G to point Finder to the path. Keep in mind that the file sizes are approximately 300MB.
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