How To Test OSX Connectivity
Understanding Internet Addressing
When connected to the Internet, an individual might receive a Public IPv4 address, such as 39.58.228.43, or an IPv6 address, like 2000:5947:7f35:c054:93e1:542d:4a9e:9ac6. The address can be checked from https://test-ipv6.com/. However, for those not well-versed in technology, communicating these addresses or MAC addresses like 14:24:d0:e1:e6:76 can be prone to errors and quickly become complex. Moreover, this method does not provide any historical data, particularly from past issues.
Navigating the World Wide Web
When attempting to access a webpage, such as https://reynolds.net, the process begins with contacting a DNS server to translate the host portion “reynolds” combined with the Top Level Domain “net” of the URL to an IP address like 90.45.222.192. Each web request from your computer and browser includes its type, 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 Significance of Default Gateways
The default gateway is typically an address that is automatically configured via DHCP. An example of the default gateway is 192.0.0.10, with addresses usually ending in .1 or .254 based on the scope size, where the computer routes all its traffic. For more information on setting up IPv6 connectivity, a comprehensive guide is available at how-to-fix-ipv6-connectivity/. On Mac or Linux, verification can be done using the following command:
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 192.0.0.10 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:d8ca:1934:db77:6b09%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): {86.148.242.216, 244.251.28.228}
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 14:24:d0:e1:e6:76
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 37:06:fc:2e:aa:ad
}
Fixing Issues with Wired and Wireless Connections
When it comes to sending data to your router, you might be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of which version of OSX/macOS you have, whether it’s 10.12.2, 11.3.7, or 12.2.6, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting comes in handy, especially for teams that adopt remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One of the helpful tools on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI, and can be configured to generate specific troubleshooting logs. In addition, the sysdiagnose tool can be used to generate 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 write logs to /var/tmp/<blah>.tar.gz. Alternatively, you can run sudo /usr/bin/sysdiagnose interactively, which will prompt a privacy warning and open Finder in the correct location. Be mindful of the file sizes, which can be around 300MB or more.
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