How Do You Troubleshoot MacOS Internet Connection
Functioning of Internet Addressing
When using the Internet, you are assigned a Public IPv4 address such as 172.67.135.252 or an IPv6 address such as 2000:3bdc:1aa8:e8e2:487a:4407:f281:a732. Validation of these addresses can be done at https://test-ipv6.com/. However, for those who are not technologically inclined, communicating these addresses, or MAC addresses like 6e:02:c1:ce:85:25, can be prone to error and become complicated quickly. Furthermore, it does not provide any historical data, especially for previous issues.
Navigating the Internet
Accessing a web page like https://harber.io involves initially reaching out to a DNS server to convert the host portion (harber) paired with the Top Level Domain (io) of the URL into an IP address such as 148.90.66.73. Every web request from your computer and browser is sent with its specific type, for example: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
Significance of Default Gateways
Usually, your default gateway is an automatically configured address via DHCP. Generally, you receive a default gateway such as 192.168.101.115 (though they typically end in .1 or .254 depending on the scope size), and this is where your computer directs all its traffic to be routed onwards. For IPv6, we have an in-depth guide on how-to-fix-ipv6-connectivity/, and you can check on Mac or Linux with:
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 192.168.101.115 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:af00:9b9:e663:8013%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): {132.142.141.79, 26.145.107.72}
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 6e:02:c1:ce:85:25
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 ff:0d:89:34:cf:14
}
Solve Connection Issues with Wired or Wireless Networks
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.
Troubleshooting Tips for Apple macOS / OSX
Regardless of whether you are using OSX or macOS version 10.13.1, 11.4.2, or 12.3.7, there is a variety of tools available for troubleshooting. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams that embrace remote work and Work From Anywhere (WFA).
Using Built-in Scripts for Assistance
A very useful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless-related settings to the CLI and can also be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is point-in-time data in relation to wireless, similar to wdutil.
To run it in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. For an interactive run, use sudo /usr/bin/sysdiagnose which will trigger 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 point Finder to the path. Keep in mind that the file sizes can be around 300MB.
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