How To DiagnOSe Mac No-access
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address such as 130.241.235.165 or an IPv6 address like 2000:c7eb:8e4f:ceb7:72c4:b0bf:7d48:dbec. You can verify this information by visiting https://test-ipv6.com/. However, conveying these addresses to individuals who are not tech-savvy can be error-prone and complex. Moreover, it does not provide any historical data, especially concerning past issues.
Navigating the World Wide Web
To access a website like https://roberts-beatty.com, you first connect to a DNS server to convert the host portion (roberts-beatty) along with the Top Level Domain (com) of the URL into an IP address, such as 212.141.227.125. Your computer and browser include its type in all web requests, for example Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A
Significance of Default Gateways
Your default gateway is typically an automatically assigned address through DHCP, such as 10.120.34.229 (usually ending in .1 or .254 depending on the scope size). This is where your computer sends all its traffic to be routed onwards. For IPv6, further information can be found in our in-depth analysis on how-to-fix-ipv6-connectivity/, and you can verify it on Mac or Linux with:
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 10.120.34.229 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:bacf:e959:bf8:2cd%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): {129.153.40.164, 209.204.16.184}
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 8a:a5:d8:88:dc:04
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 ae:a5:06:ba:3a:66
}
Fixing Connectivity Issues for Wired and Wireless Networks
When it comes to transferring data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Solutions for Apple macOS / OSX
Regardless of whether you are using OSX or macOS versions such as 10.11.4, 11.4.3, or 12.3.1, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a continuous set of correlated values over time. This is where automated remote troubleshooting becomes crucial, especially for remote work and Work From Anywhere (WFA) teams.
Effective Built-in Scripts
A highly useful tool in OSX/macOS is the sudo wdutil info, which provides a CLI dump of current wireless settings and can also be configured to generate specific troubleshooting logs. Additionally, the more comprehensive sysdiagnose tool can generate a wide range of logs, although many are only related to wireless at a specific point in time, similar to the wdutil tool.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz. Alternatively, if you prefer to run it interactively, you can use sudo /usr/bin/sysdiagnose, which will provide a privacy warning. If not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp using Finder with Cmd+Shift+G. Keep in mind that the file sizes are around 300MB, more or less.
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