How To Understand MacOS Connectivity

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 172.25.81.73 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. 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 172.25.81.73 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.

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  172.25.81.73    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:ddeb:83c1:acf7:27bf%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): {173.53.118.156, 205.36.250.171}
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 42:16:85:d7:22:eb
  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 8c:34:44:0a:51:97
}

Resolve Issues with Wired or Wireless Connections

When it comes to transmitting data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.

Steps to Take for Apple macOS / OSX Users

No matter which version of OSX/macOS you are operating on, whether it’s 10.13.3, 11.0.6, or 12.2.3, there are various troubleshooting tools at your disposal. However, these manual actions and scripts are unable to provide a set of interconnected values over a period of time. This is where automated remote troubleshooting becomes invaluable, particularly for teams that are embracing remote work and Work From Anywhere (WFA).

Pre-installed Scripts That Can be Beneficial

A highly useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of the current wireless settings to the CLI and can also be configured to generate specific logs for troubleshooting purposes. Moreover, the sysdiagnose tool can be utilized to generate a wide range of logs, although much of it pertains to wireless settings at a specific point in time, similar to wdutil.

By running sudo nohup /usr/bin/sysdiagnose -u &, you can execute it in the background and it will write logs to /var/tmp/<blah>.tar.gz for you. Alternatively, if you prefer to run it interactively (although there isn’t much interaction involved), you can execute
sudo /usr/bin/sysdiagnose, which will display a privacy warning. When not run in the background, it should open Finder in the appropriate location, or you can navigate to /var/tmp, or use Finder with Cmd+Shift+G to direct Finder to the path. Just be mindful of the file sizes, which are approximately 300MB give or take.

Possibly Helpful Videos

Video Title Channel
macOS Big Sur - What's New in Apple macOS 11 Hands-On Mac
Mac Activity Monitor - How to Troubleshoot Your Mac Hands-On Mac
Secret Mac Boot Commands - Mac Boot Key Combinations Hands-On Mac
On the Road to Big Sur 2 - Compatibility Hands-On Mac
Securing macOS Big Sur Hands-On Mac
Table 1.0 - Video Help



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