How To Understand MacOS Internet
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address such as 238.107.109.117 or an IPv6 address like 2000:67d7:3e4e:345d:1a95:1323:eb79:f2fa. This can be verified by visiting https://test-ipv6.com/. However, explaining and communicating these addresses, or even MAC addresses like 49:78:b5:22:ba:56, to those who are not tech-savvy can become challenging and prone to errors. Moreover, this method lacks historical data, especially during previous issues.
Navigating the World Wide Web
When attempting to access a website such as https://oreilly-hauck.com, your computer first contacts a DNS server to translate the host portion (oreilly-hauck) together with the Top Level Domain (com) of the URL to an IP address like 27.25.37.128. Additionally, your computer and browser share its specifications with all web requests, for example: 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
The default gateway is typically an automatically assigned address via DHCP, such as 192.168.136.185 (although they usually end in .1 or .254 depending on the scope size). This is where your computer sends all its traffic to be routed onwards. For IPv6, detailed instructions can be found on how-to-fix-ipv6-connectivity/, or alternatively you can check on Mac or Linux by using the following:
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 192.168.136.185 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:d6dc:45fd:aa11:50c6%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): {238.12.204.181, 163.138.246.2}
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 49:78:b5:22:ba: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 3e:9e:00:df:50:00
}
Resolving Connection Issues for Wired and Wireless Networks
When it comes to transmitting data to your router, you have the option of using either 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 or macOS version 10.14.7, 11.1.8, or 12.1.1, there are various tools available for troubleshooting. 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 operate in remote work environments and embrace the concept of Work From Anywhere (WFA).
Utilizing Built-in Scripts for Assistance
One useful tool on OSX/macOS is sudo wdutil info, which provides a comprehensive dump of current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting purposes. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is related to wireless settings at a specific point in time, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively, you can execute sudo /usr/bin/sysdiagnose, which will prompt 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 or use the path. However, be mindful of the file sizes, which are typically around 300MB.
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