How Do You Test MacOS Connectivity
Understanding Internet Address Allocation
When using the Internet, individuals are assigned either a Public IPv4 address, such as 69.215.39.5, or an IPv6 address, like 2000:ce22:fa3f:1600:b65:4ca2:8550:d58c. The validity of these addresses can be verified through https://test-ipv6.com/. However, for those who are not technologically savvy, conveying these addresses or MAC addresses such as 3a:b5:c8:ea:f8:a0 can be prone to errors and quickly become complex. Moreover, this method does not provide any historical data, particularly for resolving past issues.
Navigating Website Access
In order to reach a webpage, such as https://fisher-cormier.org, the initial step involves accessing a DNS server to convert the host portion (fisher-cormier) along with the Top Level Domain (org) of the URL, to an IP address like 191.126.117.100. Moreover, a computer and browser disclose its specifications with every web request, for example:
Mozilla/5.0 (Windows; U; Win 9x 4.90; SG; rv:1.9.2.4) Gecko/20101104 Netscape/9.1.0285
Understanding the Significance of Default Gateways
The default gateway is typically an automatically configured address obtained through DHCP. This gateway is usually in the form of an address such as 10.67.64.57 (often ending in .1 or .254 based on the scope size), and serves as the point where a computer sends all its traffic to be routed to other destinations. For IPv6, detailed instructions on how to resolve connectivity issues can be found at how-to-fix-ipv6-connectivity/, and can also be checked on Mac or Linux using the following method:
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 10.67.64.57 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 fe80:8d19:3b16:c7e0:4771%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): {38.145.8.137, 241.111.33.247}
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 3a:b5:c8:ea:f8:a0
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 d4:24:85:97:e9:9c
}
Solutions for Wired and Wireless Connectivity Issues
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 Techniques for Apple macOS / OSX
Regardless of whether you are using OSX/macOS versions like 10.15.7, 11.3.9, or 12.3.5, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a comprehensive set of correlated values over a period of time. This is where automated remote troubleshooting becomes invaluable, especially for teams that are engaged in remote work and Work From Anywhere (WFA).
Useful Built-in Utilities
One incredibly useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless related settings to the command line interface (CLI). This can also be configured to generate specific logs for troubleshooting purposes. Furthermore, the sysdiagnose tool offers a more comprehensive solution by generating a wide range of logs, although much of it is only relevant to wireless networks, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & will execute it in the background and save the logs to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively (although there isn’t much interaction), you can use the commandsudo /usr/bin/sysdiagnose, which will prompt a privacy warning. When not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp using Cmd+Shift+G in Finder. Keep in mind that the file sizes are around 300MB.
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