DiagnOSe OSX No-access
Explanation of Internet Addressing
When using the internet, you will have a Public IPv4 address, such as 162.170.231.40, or an IPv6 address, like 2000:46c1:95aa:f13a:f43b:ad8a:d1e0:31af. This can be verified on https://test-ipv6.com/. However, it can be challenging for individuals who are not technically inclined to communicate these addresses or MAC addresses like 68:db:34:8a:07:94. Additionally, the lack of historical data from previous issues adds to the complexity.
Steps to Access the Internet
When accessing a web page, such as https://collins.io, the first step is to connect to a DNS server in order to translate the host portion (collins) combined with the Top Level Domain (io) of the URL into an IP address, such as 192.214.23.237. Your computer and browser send its type with all web requests, for example, Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
The Significance of Default Gateways
The default gateway is typically an automatically configured address via DHCP. This gateway, such as 10.229.139.175 (although they generally end in .1 or .254 depending on the scope size), is where your computer sends all its traffic to be routed onwards. For IPv6, there is an in-depth guide on how-to-fix-ipv6-connectivity/, and on Mac or Linux, it can be checked by using the following command:
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 10.229.139.175 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 fe80:9789:f3c4:69fe:befe%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): {110.96.236.240, 3.234.22.34}
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 68:db:34:8a:07:94
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 47:ec:20:d1:1d:ea
}
Fixing Issues with Wired and Wireless Connections
When transmitting data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Methods for Apple macOS / OSX
Regardless of whether you are on OSX/macOS version 10.15.4, 11.0.9, or 12.2.1, there are various tools available for troubleshooting. However, manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes advantageous, especially for teams that are engaged in remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts for Assistance
On OSX/macOS, the sudo wdutil info tool is quite useful as it provides a current wireless related settings dump to the CLI, and it can be configured to generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant to wireless at specific points in time, like wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz for you. Alternatively, running sudo /usr/bin/sysdiagnose interactively will give a privacy warning, and 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. However, be cautious of the file sizes, which can be around 300MB or slightly more.
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