How To Support Mac Internet Connection

Understanding Internet Addressing

When connecting to the Internet, you are typically assigned either a Public IPv4 address, such as 49.183.216.134, or an IPv6 address like 2000:a468:c08d:f17d:207:6dcf:aaf8:e0c. This information can be verified by visiting https://test-ipv6.com/. However, for individuals who are not well-versed in technology, conveying or discussing these addresses, or even referring to MAC addresses like c0:3f:b8:cf:9d:82, can be prone to errors and become complex. Furthermore, this does not provide any historical data, especially when past issues occurred.

Navigating the World Wide Web

When attempting to access a webpage, such as https://morissette.org, the first step is to contact a DNS server to convert the host portion (morissette) combined with the Top Level Domain (org) of the URL into an IP address, for example, 35.253.243.213. Additionally, your computer and browser include its type in all web requests, such as
Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0

Understanding the Significance of Default Gateways

Usually, your default gateway is automatically configured through DHCP. This gateway typically comes in the form of an address like 172.29.60.115 (although they often end in .1 or .254 depending on the scope size) and it is where your computer forwards all of its traffic to be routed further. For IPv6, a comprehensive guide is available at how-to-fix-ipv6-connectivity/, although it is also possible to check on Mac or Linux using the following command:

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  172.29.60.115    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   fe80:1570:6b7c:a96e:1e13%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): {228.98.25.2, 187.66.156.156}
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 c0:3f:b8:cf:9d:82
  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 be:1d:41:52:96:ac
}

Diagnosing Connectivity Issues for Wired and Wireless Networks

When it comes to transmitting data, you have the option of using a wired or wireless (Wi-Fi) medium at the physical and data layer to send information to your router.

Troubleshooting Strategies for Apple Devices Running macOS / OSX

Regardless of whether your device is running OSX/macOS version 10.15.5, 11.4.7, or 12.2.2, there are various tools available for troubleshooting connectivity issues. However, manual actions and scripts alone do not provide a comprehensive overview of correlated values over time. This is where automated remote troubleshooting becomes invaluable, particularly for teams that operate remotely or embrace a Work From Anywhere (WFA) model.

Effective Built-in Tools for Troubleshooting

A useful tool for OSX/macOS is the sudo wdutil info command, which provides a comprehensive dump of current wireless settings to the command line interface. It can also be configured to generate specific logs for troubleshooting purposes. Another comprehensive tool is the sysdiagnose tool, which can generate a wide range of logs, although some of the information is only relevant to wireless settings, similar to wdutil.

To run it in the background and generate logs in /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 (although it comes with a privacy warning). When run interactively, 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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