How To DiagnOSe Mac Internet
Overview of Internet Addressing
When using the Internet, you are assigned a Public IPv4 or IPv6 address, such as 68.149.12.112 or 2000:c52e:9417:fb74:d888:cf73:f1d9:5a9a. You can verify your address at https://test-ipv6.com/. However, conveying these complex addresses to those who are not technologically savvy, or even discussing MAC addresses like 4e:53:7a:34:12:81, can be prone to errors and quickly become convoluted. Moreover, this method does not provide any historical data, especially for past issues.
Navigating the World Wide Web
In order to access a website, such as https://nitzsche-schoen.org, you initially connect to a DNS server to convert the host portion (nitzsche-schoen) combined with the Top Level Domain (org) of the URL to an IP address, like 71.22.50.201. Your computer and browser automatically transmit its type with every web request, for example: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
Understanding the Significance of Default Gateways
The default gateway is typically an address configured automatically via DHCP. You are assigned a default gateway, such as 172.19.229.199 (although they typically end in .1 or .254 depending on the scope size), and this is the destination where your computer sends all of its traffic to be routed further. For IPv6, a more detailed explanation is available at how-to-fix-ipv6-connectivity/ but it can also be verified 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 172.19.229.199 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:d4bb:30a1:b495:3950%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): {39.188.151.171, 156.183.153.135}
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 4e:53:7a:34:12:81
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 0a:cf:02:34:e3:d6
}
Solutions for Connectivity Issues
When it comes to transmitting data to your router, the choice of using a wired or wireless (Wi-Fi) medium happens at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
No matter if your system is running OSX/macOS versions like 10.11.9, 11.2.6, or 12.2.2, there are various tools available for solving connectivity issues. However, the manual actions and scripts might lack the ability to provide a series of correlated values over time. In such cases, automated remote troubleshooting becomes indispensable, especially for teams adopting remote work and Work From Anywhere (WFA) policies.
Utilizing Built-in Scripts
One of the useful tools 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 logs for troubleshooting. Alternatively, the sysdiagnose tool can be used to produce a wide range of logs, although much of the data is only relevant at a specific point in time in relation to wireless, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will generate logs in /var/tmp/<blah>.tar.gz for you. For an interactive run (although there isn’t much interaction), you can execute sudo /usr/bin/sysdiagnose with a privacy warning. Running it without the background option should open Finder in the correct location, or you can navigate to /var/tmp manually, or use Cmd+Shift+G in Finder to navigate to the path. Keep in mind that the file sizes are approximately 300MB.
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