How Do You DiagnOSe OSX Internet
Explaining the Functionality of Internet Addressing
When using the Internet, individuals may be assigned a Public IPv4 address, such as 199.140.219.24, or an IPv6 address, like 2000:5d3:b83:66bd:846e:7a03:9b6d:7759. These addresses can be verified at https://test-ipv6.com/. However, for those who are not tech-savvy, conveying these addresses or even referencing MAC addresses, such as 5d:53:a9:84:79:8e, can lead to errors and complications. Furthermore, this method does not provide any historical data, especially in cases of past issues.
Navigating the Internet
When attempting to access a webpage, like https://johnson.info, the first step involves contacting a DNS server to convert the combination of the host portion (johnson) and the URL’s Top Level Domain (info) into an IP address, such as 59.39.179.49. In all web requests, the computer and browser communicate their type, for example: Mozilla/5.0 (Windows; U; Win 9x 4.90; SG; rv:1.9.2.4) Gecko/20101104 Netscape/9.1.0285
Understanding the Significance of Default Gateways
Typically obtained automatically through DHCP, the default gateway is an essential component. It is represented by an address like 192.0.0.160 (commonly ending in .1 or .254, based on the scope size), and serves as the routing destination for all traffic originating from the computer. For a detailed guide on IPv6, refer to how-to-fix-ipv6-connectivity/. On Mac or Linux, the gateway can be verified 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 192.0.0.160 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:aa62:bdff:83c2:dbb1%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): {102.34.211.24, 183.90.8.32}
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 5d:53:a9:84:79:8e
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 24:fb:93:91:84:ac
}
How to Resolve Issues with Wired and Wireless Connections
When transferring data to your router, you may utilize either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Tips for Troubleshooting on Apple macOS / OSX
Regardless of whether you are running OSX/macOS versions such as 10.15.6, 11.3.4, or 12.2.3, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes valuable, especially for teams that embrace remote work and Work From Anywhere (WFA).
Using In-Built Scripts for Assistance
A highly useful tool on OSX/macOS is the sudo wdutil info, which provides a dump of current wireless-related settings to the CLI, and it can also be configured to generate specific logs for troubleshooting purposes. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant to wireless settings just like wdutil.
By running sudo nohup /usr/bin/sysdiagnose -u & in the background, the tool will write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively, you can execute sudo /usr/bin/sysdiagnose, which will prompt a privacy warning. When not run in the background, it should open Finder in the correct location, allowing you to navigate to /var/tmp or use Finder with Cmd+Shift+G to point Finder to the path. Keep in mind that the file sizes are approximately 300MB.
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