How Can I Troubleshoot Apple No-access
Understanding Internet Addressing
When using the Internet, you may be assigned a Public IPv4 address such as 111.4.99.253 or an IPv6 address like 2000:6e24:d942:a948:e4a9:6a57:e222:33d8. This information can be verified at https://test-ipv6.com/. However, expressing these addresses or MAC addresses like 1c:07:28:74:d8:2e to those who are not technologically inclined can be prone to mistakes and can become complex. Furthermore, this method does not provide any historical data, particularly when issues have occurred in the past.
Navigating Through the Internet
Accessing a website such as https://hudson.co involves accessing a DNS server to translate the host portion (hudson) along with the Top Level Domain (co) of the URL to an IP address like 120.238.168.31. With every web request, your computer and browser include its 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 Default Gateways
Your default gateway is usually an automatically configured address via DHCP. This default gateway, such as 10.201.121.183, serves as the outbound routing destination for all the traffic from your computer. In the case of IPv6, a more detailed explanation can be found at how-to-fix-ipv6-connectivity/, but on Mac or Linux, it can be checked by:
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 10.201.121.183 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:ef2c:ce5e:2e97:17f3%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): {228.204.241.184, 13.151.59.97}
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 1c:07:28:74:d8:2e
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 ce:ee:77:2a:d3:a2
}
Resolving Issues with Wired and Wireless Connections
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.
Effective Steps for Apple macOS / OSX Users
No matter which version of OSX/macOS you are currently using - be it 10.12.3, 11.1.8, or 12.2.9, 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 invaluable, especially for teams that have embraced remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One highly effective tool on OSX/macOS is the sudo wdutil info, which provides a dump of current wireless related settings to the CLI and 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 point-in-time related to wireless, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & will execute it in the background and write logs to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively, you can use sudo /usr/bin/sysdiagnose, which will prompt a privacy warning. Running it in the foreground should open Finder in the correct location, or you can navigate to /var/tmp using Finder or use Cmd+Shift+G to point Finder to the path. Keep in mind that the file sizes are approximately 300MB.
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