How To Understand Mac Internet
Understanding Internet Addressing
When using the Internet, you are assigned a unique identifier known as an IP address. This can be a public IPv4 address, such as 112.175.210.17, or an IPv6 address like 2000:b8b4:21a6:9a1f:b2e5:dd80:3861:1b57. You can check your IP address using a tool like https://test-ipv6.com/. However, communicating these addresses, or even MAC addresses like b6:a3:f9:ba:c3:9d, can be complex and error-prone for non-technical users. Additionally, this method does not provide any historical data.
Navigating the World Wide Web
Accessing a specific web page, such as https://jerde.biz, requires the translation of the host portion (jerde) combined with the Top Level Domain (biz) of the URL into an IP address like 123.16.242.235. Your computer and browser also send their specifications with every web request, such as Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16.
Understanding Default Gateways
The default gateway, usually configured automatically via DHCP, is the point to which your computer sends all its network traffic for routing onwards. This gateway is typically assigned an address like 172.22.231.78 (although they often end in .1 or .254 depending on the scope size). For IPv6, a comprehensive guide on this topic can be found at how-to-fix-ipv6-connectivity/, and Mac or Linux users can check their default gateway using specific commands.
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 172.22.231.78 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 fe80:6de4:4623:b488:75ed%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): {22.215.29.118, 216.219.39.205}
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 b6:a3:f9:ba:c3:9d
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 36:2a:aa:a0:31:1f
}
Resolving Issues with Your Wired or Wireless Connection
When transmitting data to your router, you might be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Steps to Take for Apple macOS / OSX Users
Regardless of whether you are using OSX/macos version 10.12.9, 11.2.1, or 12.0.7, there are various troubleshooting tools available. However, these manual methods and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams that are embracing remote work and the Work From Anywhere (WFA) concept.
Useful Built-in Scripts
One useful tool on OSX/macos is the sudo wdutil info, which provides a dump of the current wireless settings to the CLI and can also be configured to generate specific logs for troubleshooting. Another comprehensive tool is the sysdiagnose, which can generate a wide range of logs, although many are only relevant to the wireless network at a specific point in time, similar to wdutil.
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, you can use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can use sudo /usr/bin/sysdiagnose, which will give a privacy warning. When 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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