How Do You Troubleshoot Apple No-access
Understanding the Function of Internet Addressing
When using the Internet, individuals are assigned Public IPv4 and IPv6 addresses to enable communication and connectivity. For example, a Public IPv4 address may appear as 192.76.212.193 while an IPv6 address may appear as 2000:f5e0:addb:d128:35:7192:5494:cd01. These addresses can be verified using https://test-ipv6.com/. However, conveying these addresses to non-technical individuals or referencing MAC addresses such as 91:b4:d2:d5:40:67 can be prone to errors and complexity. Also, this method does not provide any historical data, particularly regarding past issues.
Navigating the World Wide Web
When attempting to access a webpage like https://lind-bruen.biz, the initial step involves consulting a DNS server to convert the host portion (lind-bruen) combined with the Top Level Domain (biz) into an IP address, such as 103.106.122.49. Interestingly, every web request contains information about the computer and browser type, for instance: Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
Understanding the Significance of Default Gateways
The default gateway typically receives an automatically configured address via DHCP, resulting in an address like 10.117.165.56 (although often ending in .1 or .254 based on the scope size). This default gateway is where a computer sends all its traffic to be routed onwards. For IPv6 troubleshooting, there is a comprehensive guide available at how-to-fix-ipv6-connectivity/. Moreover, users can verify this information on Mac or Linux platforms using the following methods:
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 10.117.165.56 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:b9b2:257:aa17:eee7%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): {236.91.220.218, 201.65.23.175}
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 91:b4:d2:d5:40:67
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 5d:36:24:ef:9f:a2
}
Solutions for Resolving Wired and Wireless Issues
When it comes to transmitting data to your router, you may be utilizing a wired or wireless (Wi-Fi) medium at the physical and data layer.
Tips and Tricks for Apple macOS / OSX Users
No matter which version of OSX/macOS you’re running, whether it’s 10.14.7, 11.0.7, or 12.1.9, there is a variety of troubleshooting tools available. However, these manual actions and scripts don’t provide a set of correlated values over time which is where remote troubleshooting becomes essential, especially for teams that operate remotely and embrace the Work From Anywhere (WFA) approach.
Useful Built-in Scripts
On OSX/macOS, the sudo wdutil info tool is incredibly useful as it provides current wireless settings and can also be configured to generate specific troubleshooting logs. In addition, the sysdiagnose tool is even more comprehensive as it can generate a wide range of logs, although it is mostly point-in-time in relation to wireless, similar to wdutil.
To run sudo nohup /usr/bin/sysdiagnose -u & in the background and write logs to /var/tmp/<blah>.tar.gz, or to run it interactively, users can execute sudo /usr/bin/sysdiagnose with a privacy warning. When not run in the background, it should open Finder in the correct location, or users can navigate to /var/tmp or use Finder with Cmd+Shift+G to locate the path. However, keep in mind that the file sizes can be around 300MB.
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