How Can I Understand Mac Connectivity
Functioning of Internet Addressing
When using the internet, one may have a Public IPv4 address such as 167.125.179.160 or an IPv6 address like 2000:eea7:ece9:1cf4:3c70:e8f8:c59b:dd2b. This can be verified using https://test-ipv6.com/. However, for those who are not technically inclined, attempting to communicate these addresses, or even calling out MAC addresses like 4a:45:5a:00:0b:28, can be prone to errors and become complex rapidly. Furthermore, this does not provide any historical data (especially from past issues).
Navigating the Internet
To access a web page such as https://ritchie-kuphal.com, the first step is to request the assistance of a DNS server to convert the host portion (ritchie-kuphal) combined with the Top Level Domain (com) of the URL, to an IP address like 16.242.38.65. Every web request from your computer and browser includes its type, for example: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A
Significance of Default Gateways
Your default gateway is typically an automatically configured address via DHCP. It is assigned a default gateway, such as 192.0.0.30 (usually ending in .1 or .254 based on the scope size), where your computer directs all its traffic to be routed. For IPv6, there is an in-depth explanation in the article how-to-fix-ipv6-connectivity/, but the verification can be done on Mac or Linux with the following steps:
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 192.0.0.30 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 fe80:869c:75b:3576:8d7b%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): {87.230.193.9, 224.227.185.73}
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 4a:45:5a:00:0b:28
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 26:bc:5c:3f:21:de
}
Fixing Connectivity Issues on Wired or Wireless Networks
When it comes to transmitting data to your router, you might be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
No matter which version of OSX/macOS you are currently using, whether it’s 10.13.5, 11.3.8, or 12.0.5, there are various troubleshooting tools available. Despite the availability of manual actions and scripts, they 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 Work From Anywhere (WFA).
Utilizing Built-in Scripts for Assistance
A very useful 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 purposes. 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, just like wdutil.
To run it 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 the command 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 to locate the path. It’s important to be aware of the file sizes, which are approximately 300MB more or less.
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