How Can I DiagnOSe OSX Internet Connection
Understanding Internet Addressing
When using the Internet, you are assigned a public IP address, which can be in the form of either IPv4 like 162.121.21.160 or IPv6 like 2000:8c:640d:9012:7a3e:5c8a:42eb:b2d2. You can verify this information by visiting https://test-ipv6.com/. However, conveying these addresses to individuals with limited technical knowledge or discussing MAC addresses such as 50:80:db:9b:a7:1f can quickly become complicated and prone to errors. Moreover, this method does not provide any historical data, particularly from previous issues.
Navigating the World Wide Web
To access a webpage such as https://wyman.name, your system initially contacts a DNS server to convert the host section (wyman) along with the Top Level Domain (name) of the URL into an IP address, for example, 116.156.8.224. Every time your computer or browser sends a web request, it also includes its specific type, such as Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16.
Understanding the Significance of Default Gateways
Your default gateway is typically an automatically assigned address through DHCP, and it usually ends with .1 or .254 depending on the scope size, such as 10.99.116.195. This is where your computer directs all its traffic for onward routing. For IPv6, a comprehensive explanation can be found at how-to-fix-ipv6-connectivity/. On Mac or Linux, you can verify this using:
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 10.99.116.195 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:f8f4:c8dd:120e:dd91%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): {218.113.26.220, 143.124.108.138}
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 50:80:db:9b:a7:1f
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 be:4f:8a:d3:77:f8
}
Resolving Issues with Wired and Wireless Connectivity
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 Users
Regardless of the version of OSX/macOS you are running, whether it’s 10.15.2, 11.6.3, or 12.3.3, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes essential, particularly for teams that are engaged in remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts for Assistance
One useful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings on the CLI, and can also be configured to generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs, although many of them are only point-in-time 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 sudo /usr/bin/sysdiagnose (although there is minimal interaction) and be aware of the large file sizes, usually around 300MB.
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