How Can I Understand MacOS Connectivity

Understanding Internet Addressing

When you connect to the Internet, you receive a Public IPv4 address such as 146.46.251.47 or an IPv6 address like 2000:fea:271:f1a9:6254:fee7:d30:80e2. You can verify this by visiting https://test-ipv6.com/. Translating and communicating these addresses, along with MAC addresses like cc:77:5f:4d:55:a6, can be challenging for those not well-versed in tech, and it fails to provide historical data.

Navigating the World Wide Web

Accessing a webpage such as https://rolfson.name involves initially accessing a DNS server to convert the host portion (rolfson) combined with the Top Level Domain (name) of the URL to an IP address like 183.164.121.24. Your computer and browser send their types with all web requests, for instance:
Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36

The Significance of Default Gateways

Generally, your default gateway is an automatically configured address through DHCP. This could be a default gateway like 10.255.70.67 (often ending in .1 or .254 based on scope size), where your computer directs all its traffic to be routed onwards. For IPv6, detailed instructions can be found in our article how-to-fix-ipv6-connectivity/, but you can verify on Mac or Linux using:

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  10.255.70.67    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:dd01:8971:a1c1:48a9%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): {158.33.184.187, 65.190.138.98}
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 cc:77:5f:4d:55:a6
  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 e5:16:9e:24:55:0e
}

Resolve Issues with Wired or Wireless Connections

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

Troubleshooting Tips for Apple macOS / OSX Devices

Regardless of whether you are running OSX/macOS version 10.12.9, 11.0.7, or 12.1.7, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes valuable, especially for teams that are adopting remote work and Work From Anywhere (WFA).

Utilizing Built-in Scripts for Assistance

On OSX/macOS, the sudo wdutil info tool is quite useful as it provides a dump of current wireless-related settings to the CLI, and can also be configured to generate specific troubleshooting logs. Additionally, the sysdiagnose tool, while perhaps more comprehensive, can be used to generate a wide range of logs, although much of it is specific to wireless and is similar to wdutil.

To run sudo nohup /usr/bin/sysdiagnose -u & in the background and generate logs in /var/tmp/<blah>.tar.gz. Alternatively, for an interactive execution (with minimal interaction), run sudo /usr/bin/sysdiagnose, which will prompt a privacy warning. If not run in the background, it should open Finder in the correct location, allowing navigation to /var/tmp or using Finder with Cmd+Shift+G to locate the path. Keep in mind that the file sizes are approximately 300MB.

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