How To Troubleshoot MacOS Internet Connection
Understanding the Functionality of Internet Addressing
When on the Internet, you are assigned either a Public IPv4 address, such as 199.91.197.135, or an IPv6 address, like 2000:c0d4:b280:1f47:beb:512e:49a4:306a. Verification of this information can be performed at https://test-ipv6.com/. However, for individuals not well-versed in technology, attempting to communicate or identify addresses, such as MAC addresses, can be prone to errors and complications. Additionally, this method does not provide any historical data, particularly from previous issues.
Navigating the World Wide Web
In order to access a website, such as https://purdy.co, the first step involves consulting a DNS server to convert the host portion (purdy) combined with the Top Level Domain (co) of the URL into an IP address, such as 170.131.197.55. Furthermore, your computer and browser transmit its type with all web requests, for example, 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
Typically, your default gateway is an automatically configured address via DHCP, resulting in a default gateway like 172.16.156.25 (usually ending in .1 or .254, depending on the scope size). This is where your computer forwards all its traffic to be routed onwards. For IPv6, a comprehensive overview is available at how-to-fix-ipv6-connectivity/, but you can verify on Mac or Linux using the 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 172.16.156.25 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 fe80:68b2:c13a:ea1b:2c9a%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): {180.140.118.223, 21.187.155.116}
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 62:1a:d4:19:2b:fa
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 48:4f:dd:f2:6a:21
}
Resolving Connection Issues for Wired or Wireless Networks
In your network setup, whether using a wired or wireless (Wi-Fi) medium, you may encounter issues when sending data to your router.
Troubleshooting on Apple macOS / OSX
Regardless of the version of OSX/macOS you are running, be it 10.14.5, 11.1.7, or 12.0.3, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time. Therefore, automated remote troubleshooting becomes invaluable, particularly for teams that embrace remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts for Assistance
An extremely useful tool on OSX/macOS is the 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 offers a more comprehensive option for generating a wide range of logs related to wireless issues, although much of it is only point-in-time data, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively, you can execute sudo /usr/bin/sysdiagnose, which will provide 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. It’s important to note that the file sizes are approximately 300MB.
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