How Do You Understand MacOS No-access
Demystifying Internet Addressing
When using the internet, you are assigned a Public IPv4 address or an IPv6 address, such as 46.183.66.221 and 2000:2e63:2b69:6ed8:27c2:150f:e4e2:df37, respectively. You can verify this information on https://test-ipv6.com/. However, explaining and communicating these complex addresses, and even MAC addresses like 71:66:16:f4:8d:e1, can be challenging, especially for those who are not technically inclined. Furthermore, this method does not provide historical data, particularly for previous issues.
Understanding Web Access
When attempting to access a webpage, such as https://schmitt.net, your computer first contacts a DNS server to convert the host name (schmitt) in combination with the Top Level Domain (net) of the URL into an IP address, for example, 0.104.249.52. Notably, your computer and browser include its type in all web requests, for instance:
Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
Significance of Default Gateways
The default gateway typically receives an automatically configured address through DHCP. This default gateway, such as 172.30.145.73 (often ending in .1 or .254 based on the scope size), serves as the central point where your computer sends all its traffic to be routed further. For IPv6, a detailed explanation is available in how-to-fix-ipv6-connectivity/, and you can verify this on a Mac or Linux using the following command:
```bash
command here
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 172.30.145.73 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:ef8:77de:b5f5:e9bc%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): {1.209.144.86, 68.94.175.204}
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 71:66:16:f4:8d:e1
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 67:9e:01:0c:0a:a6
}
Resolve Issues with Wired and Wireless Connections
When it comes to transferring data to your router, you might be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Actions to Take for Apple macOS / OSX Users
Regardless of whether you are running 10.11.7, 11.5.6, or 12.0.5, there are various troubleshooting tools available for OSX/macOS. However, these manual procedures and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams that have adopted remote work and the Work From Anywhere (WFA) approach.
Useful Built-in Scripts
One valuable tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI and can also be configured to generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs, although most of them are point-in-time only in relation to wireless, similar to wdutil.
To run it in the background and write logs to /var/tmp/<blah>.tar.gz, use sudo nohup /usr/bin/sysdiagnose -u &. Alternatively, for a more interactive experience, you can run sudo /usr/bin/sysdiagnose, which will issue a privacy warning. When not run in the background, it should open the Finder in the correct location, allowing you to navigate to /var/tmp 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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