How To DiagnOSe MacOS No-access
The Functionality of Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 96.7.4.215, or an IPv6 address like 2000:b28:1403:90c:a02:434d:11ae:64fb. You can verify this information on https://test-ipv6.com/. However, attempting to communicate these addresses to individuals who are not tech-savvy, or even mentioning MAC addresses like 37:30:f6:d0:79:9b, can be prone to errors and becomes complex rather quickly. Furthermore, this information does not provide any historical data, especially from previous issues.
Navigating the Internet
When attempting to access a website such as https://johnston-lesch.name, you first reach out to a DNS server to convert the host portion (johnston-lesch) together with the Top Level Domain (name) of the URL to an IP address like 209.225.148.182. Your computer and browser specify the type in 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
Normally, your default gateway is automatically configured through DHCP and may be assigned a default gateway such as 10.50.12.28 (typically ending in .1 or .254 depending on the scope size). This is where your computer directs all its traffic to be routed onwards. For IPv6, more detailed information can be found in a deep dive on how-to-fix-ipv6-connectivity/, or it can 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 10.50.12.28 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:a9d2:f902:8a33:fd29%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): {26.245.94.76, 225.186.210.162}
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 37:30:f6:d0:79:9b
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 9c:c5:4d:71:67:77
}
Fixing Connectivity 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.
Tips for Troubleshooting on Apple macOS / OSX
Regardless of whether you are running on OSX/macOS versions such as 10.12.6, 11.2.3, or 12.3.6, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes valuable, especially for teams that are embracing remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts for Assistance
One beneficial tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI, and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, but much of it is only relevant to wireless on a point-in-time basis, similar to wdutil.
To run it in the background, use sudo nohup /usr/bin/sysdiagnose -u &, which will write logs to /var/tmp/<blah>.tar.gz. Alternatively, for an interactive experience (although there is not much interaction), you can run sudo /usr/bin/sysdiagnose, which will give a privacy warning. When not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp or use Finder with Cmd+Shift+G to point Finder to the path. Be cautious of the file sizes, which are approximately 300MB.
Possibly Helpful Videos
P.S. Tips For Remote Network and Client Support
Digital work requires reliable connectivity. Whether for low latency or regular data streams, Wi-Fi, DNS, and network issues cause teams to lose time and productivity. Even worse is when support teams waste time trying to recreate and isolate issues! See how PanSift saves time, money, and frustration on all sides with instant remote troubleshooting 🏠🏝🛰.
