Understand MacOS No-access
Functioning of Internet Addressing
In the realm of the Internet, individuals may possess a Public IPv4 address such as 28.206.243.156 or an IPv6 address such as 2000:4b95:f344:c93a:259f:81b9:d41b:cd9d. This can be verified at https://test-ipv6.com/. However, for those who are not well-versed in technology, attempting to communicate these addresses, or even calling out MAC addresses like 66:a5:86:bc:5f:0b, can be prone to errors and can become intricate rapidly. Moreover, this method does not provide any historical data (especially from previous issues).
Navigating the Internet
When attempting to reach a webpage such as https://hintz-crooks.io, the process involves accessing a DNS server to convert the host portion (hintz-crooks) combined with the Top Level Domain (io) of the URL into an IP address like 0.9.44.47. Both your computer and browser actually disclose their type with all web requests, for instance: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
Significance of Default Gateways
The default gateway is typically an automatically assigned address via DHCP. One would obtain a default gateway such as 172.25.252.155 (although they generally end in .1 or .254 depending on the scope size) and this is where the computer dispatches all its traffic to be routed onwards. For IPv6, comprehensive information can be found at how-to-fix-ipv6-connectivity/, and it is possible to verify on Mac or Linux using:
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 172.25.252.155 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 fe80:64d5:b8e8:9969:905e%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): {18.175.65.207, 208.14.98.16}
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 66:a5:86:bc:5f:0b
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 79:99:9e:54:de:c4
}
Resolving Wired and Wireless Network Issues
When it comes to sending data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Tips for Apple macOS / OSX Users
Regardless of the version of OSX or macOS you are using, whether it’s 10.11.2, 11.6.6, or 12.2.7, there are various troubleshooting tools available. However, these manual methods and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes valuable, particularly for teams that are embracing remote work and the Work From Anywhere (WFA) concept.
Useful Built-in Scripts
One useful tool for OSX/macOS users is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI, and can also be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of the information is only relevant at a specific point in time in relation to wireless, similar to wdutil.
To run sudo nohup /usr/bin/sysdiagnose -u & in the background and have it write logs to /var/tmp/<blah>.tar.gz, if you prefer to run it interactively, you can execute sudo /usr/bin/sysdiagnose, which will issue a privacy warning. When not running in the background, it should open Finder in the correct location, or you can navigate to /var/tmp or use Cmd+Shift+G in Finder to point to the path. It’s important to note that the file sizes are approximately 300MB.
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