How Do You DiagnOSe MacOS Internet
Understanding the Functioning of Internet Addressing
When using the Internet, you are assigned a Public IPv4 address such as 179.123.86.49 or an IPv6 address like 2000:6aa0:9a29:45d2:62c:5a44:cee:398b. This information can be verified at https://test-ipv6.com/. However, for individuals who are not familiar with technical details, conveying or even noting MAC addresses like 1d:34:bb:80:f9:2a can be prone to errors and can become complex quickly. Moreover, it does not provide any historical data, especially during previous incidents.
Navigating through the Internet
When attempting to access a website such as https://vonrueden.org, the first step is to connect with a DNS server in order to convert the host portion (vonrueden) along with the Top Level Domain (org) of the URL into an IP address like 180.191.43.174. In fact, every web request sent by your computer and browser includes its type, for example:
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
The default gateway is generally an address that is automatically configured through DHCP. It is a default gateway like 172.24.22.29 (though they typically end in .1 or .254 depending on the scope size), and it is where your computer sends all of its traffic to be routed onwards. For IPv6, we have an in-depth exploration available at how-to-fix-ipv6-connectivity/, but it can be checked on Mac or Linux with:
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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 172.24.22.29 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:bb51:52dd:84fc:b37b%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): {232.69.63.70, 190.219.239.116}
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 1d:34:bb:80:f9:2a
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 1b:af:b1:7b:be:5d
}
Resolving Connection Issues for Wired and Wireless Networks
When it comes to transmitting data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Effective Solutions for Apple macOS / OSX Users
Regardless of the version of OSX/macOS you are currently running, whether it’s 10.13.7, 11.6.2, or 12.1.9, there are various troubleshooting tools available. However, these tools do not provide a set of interconnected values over time, which is where automated remote troubleshooting becomes invaluable, particularly for teams working remotely and embracing a Work From Anywhere (WFA) setup.
Useful Built-in Tools for Troubleshooting
One particularly useful tool for OSX/macOS users is sudo wdutil info, which provides a comprehensive dump of the current wireless settings in the CLI and can be configured to generate specific troubleshooting logs. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs (though many are related to wireless settings and are point-in-time like wdutil).
To run sysdiagnose in the background and have it write logs to /var/tmp/<blah>.tar.gz, you can use the command sudo nohup /usr/bin/sysdiagnose -u &. Alternatively, if you prefer to run it interactively, you can use the command sudo /usr/bin/sysdiagnose, which will prompt a privacy warning. When not run in the background, the tool 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 can be around 300MB or slightly larger.
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