How To Troubleshoot Mac Internet Connection

Understanding the Functioning of Internet Addressing

When using the Internet, you are assigned either a Public IPv4 address, such as 73.239.81.243, or an IPv6 address, like 2000:cd96:9c00:c956:2163:bc21:5345:b25d. It is possible to verify this information by visiting https://test-ipv6.com/. However, for those who are not well-versed in technology, relaying or even identifying MAC addresses, such as 5a:c8:c8:1e:35:38, can be prone to errors and quickly become complex. In addition, this method does not provide any historical data, particularly from past issues.

Navigating the Internet

When accessing a website like https://willms.co, your system initially connects to a DNS server to convert the combination of the host portion (willms) and the Top Level Domain (co) of the URL into an IP address, such as 24.60.56.80. When making web requests, your computer and browser transmit information about its type, for example:
Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko

The Significance of Default Gateways

In networks, the default gateway address is typically assigned automatically through DHCP. It may look like 192.168.103.183 (usually ending in .1 or .254 based on the scope size), and serves as the point where your computer forwards all its traffic for further routing. For a detailed examination of IPv6 connectivity, refer to our in-depth guide on how-to-fix-ipv6-connectivity/. To verify on Mac or Linux, use the following command:
command to check gateway on Mac or Linux

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  192.168.103.183    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   fe80:91e8:7871:5ddf:6f88%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): {21.139.220.242, 8.248.143.32}
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 5a:c8:c8:1e:35:38
  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 30:91:b3:06:20:17
}

Resolving Connectivity 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.

Strategies for Addressing Problems on Apple macOS / OSX

Regardless of whether you are using version 10.14.9, 11.3.6, or 12.0.2 of OSX/macOS, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a set of correlated values over time. In this scenario, automated remote troubleshooting becomes essential, particularly for teams that have embraced remote work and the concept of Work From Anywhere (WFA).

Utilizing Pre-Installed Scripts for Assistance

One valuable tool on OSX/macOS is the sudo wdutil info command, which provides a dump of the current wireless-related settings to the CLI and can also be configured to generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant to a specific point in time, similar to wdutil.

Running the command sudo nohup /usr/bin/sysdiagnose -u & will execute it in the background and write logs to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively (even though there is not much interaction), 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, but be mindful of the file sizes, which are around 300MB more or less.

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