How Can I Troubleshoot Mac Internet Connection
Understanding Internet Address Allocation
When using the Internet, your device will be assigned a unique Public IPv4 or IPv6 address. These addresses, such as 196.224.72.171 or 2000:b7f0:2acc:8a88:6b2:8c9a:b3a7:51f6, can be confirmed using a tool like https://test-ipv6.com/. However, for those not familiar with technical terminology, communicating or referencing these addresses, including MAC addresses like 5d:0c:7c:9a:ab:ab, can be prone to errors and complexity. Moreover, this method does not provide any historical data, particularly when addressing past issues.
Navigating the World Wide Web
Accessing a website, such as https://dubuque.net, involves requesting an IP address from a DNS server to translate the URL’s host component (dubuque) and the Top Level Domain (net) into a specific IP address, like 76.255.188.68. Additionally, your computer and browser include its type in every web request, for instance: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36
Significance of Default Gateways
Commonly, a default gateway is an automatically configured address obtained through DHCP. This default gateway, such as 10.112.69.12 (often ending in .1 or .254 based on the scope size), is where your computer sends all outgoing traffic for further routing. For IPv6, a thorough examination can be found in our article on how-to-fix-ipv6-connectivity/, or can be checked using 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 10.112.69.12 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:ce00:b05d:67f5:b1ca%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): {101.164.87.146, 92.0.180.66}
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 5d:0c:7c:9a:ab:ab
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 f2:97:c8:21:51:40
}
Solving 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.
Tips for Apple macOS / OSX Users
Regardless of whether you are on OSX/macOS version 10.13.7, 11.2.3, or 12.2.7, there are several troubleshooting tools at your disposal. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes crucial, especially for teams that embrace remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts for Assistance
One valuable tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can be configured to generate specific troubleshooting logs. In addition, the sysdiagnose tool offers a comprehensive option for generating a wide range of logs (though it mostly provides point-in-time information related to wireless, similar to wdutil).
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, 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 or use Finder with Cmd+Shift+G to go to the path. Keep in mind that the file sizes are approximately 300MB.
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