How To Understand OSX Connectivity
The Process of Internet Addressing
When using the Internet, you will receive a Public IPv4 address such as 13.214.151.171 or an IPv6 address like 2000:1aac:2b58:5c8a:1b44:4160:2e47:bfb6. It is possible to verify this using https://test-ipv6.com/. However, for individuals who are not technically inclined, conveying these addresses, or even mentioning MAC addresses like 64:08:06:96:de:a5, can be prone to errors and quickly becomes complex. Moreover, this approach lacks historical data, particularly from past issues.
Navigating the Internet
In order to access a website like https://padberg.name, you initially connect to a DNS server to convert the host part (padberg) in combination with the Top Level Domain (name) of the URL into an IP address such as 35.68.118.240. Interestingly, your computer and browser include their type in all web requests e.g. Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
Understanding the Significance of Default Gateways
The default gateway is typically an address configured automatically via DHCP. You will receive a default gateway like 192.168.97.84 (though they often end in .1 or .254 depending on the scope size) and this is the destination where your computer sends all its traffic to be directed further. For IPv6, we have an extensive analysis on how-to-fix-ipv6-connectivity/ but you can perform a check on Mac or Linux by:
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 192.168.97.84 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:b8a4:63d8:91d8:bebd%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): {75.23.117.31, 5.85.212.158}
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 64:08:06:96:de:a5
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 20:fc:fa:00:90:f4
}
Resolving Connectivity Issues for Wired and Wireless Networks
When it comes to transferring data to your router, you may be utilizing a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of whether you are using OSX/macOS versions such as 10.14.4, 11.0.7, or 12.1.8, there are various troubleshooting tools available. However, these manual actions and scripts fail to provide a series of correlated values over time. Automated remote troubleshooting emerges as a valuable solution, particularly for teams that adopt remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
An invaluable tool on OSX/macOS is sudo wdutil info, which generates a dump of current wireless settings to the CLI and can also produce specific logs for troubleshooting. Furthermore, the sysdiagnose tool offers a more comprehensive option for generating a wide range of logs, although many of these are only relevant to wireless settings, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz. For an interactive approach, you can run sudo /usr/bin/sysdiagnose, which will display a privacy warning and open Finder in the correct location. Alternatively, 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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