How To Test Mac Connectivity
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address such as 27.187.218.93 or an IPv6 address like 2000:fb16:8627:e1ff:bda:449e:a4a3:cdf4. This information can be checked at https://test-ipv6.com/. Communicating these addresses, or even identifying MAC addresses like e8:13:e7:cf:bc:9b, can be challenging for those not well-versed in technology, and can quickly become complex. Furthermore, it does not provide any historical data, especially for previous issues.
Navigating the World Wide Web
Accessing a web page like https://bednar.biz involves initially contacting a DNS server to convert the host portion (bednar) and the Top Level Domain (biz) of the URL into an IP address, such as 61.60.208.10. Your computer and browser includes its type with 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
The Role of Default Gateways
The default gateway is typically an address configured automatically via DHCP, such as 10.107.120.144 (normally ending in .1 or .254 depending on the scope size), to where your computer sends all its traffic to be routed onwards. For IPv6, a detailed guide is available at how-to-fix-ipv6-connectivity/ but can also be checked 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 10.107.120.144 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 fe80:5b4a:bb42:1237:7f22%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): {35.83.132.202, 146.36.44.17}
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 e8:13:e7:cf:bc:9b
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 7a:48:f6:8c:6c:49
}
Resolving Connectivity Issues for Wired and Wireless Networks
When it comes to transmitting data to your router, you might be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of the version of OSX or macOS you are currently running, whether it’s 10.12.6, 11.5.9, or 12.1.5, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes particularly valuable, especially for teams that are embracing remote work and the Work From Anywhere (WFA) concept.
Utilizing In-Built Scripts for Assistance
A highly useful tool for OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless related settings to the CLI and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool offers a more comprehensive option, generating a wide range of logs (although much of it is only relevant to wireless settings, 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, or to run it interactively with sudo /usr/bin/sysdiagnose (which will provide a privacy warning), and access the logs in /var/tmp, keeping in mind that the file sizes are approximately 300MB.
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