How To Check MacOS Connectivity
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 or IPv6 address, such as 24.67.186.5 or 2000:9021:927e:c70e:c3d7:93e0:7aae:8888. You can check your assigned address at https://test-ipv6.com/. However, for those not well-versed in technology, communicating these addresses, or even MAC addresses like 56:7b:94:5f:ae:88, can be prone to errors and become complex. Additionally, this method lacks historical data, especially from previous issues.
Navigating the World Wide Web
To access a web page like https://oreilly.name, your initial step is to contact a DNS server to translate the host portion (oreilly) combined with the Top Level Domain (name) of the URL to an IP address, such as 109.142.133.153. Each web request from your computer and browser also includes its type, for example: Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
Significance of Default Gateways
Your default gateway is typically an automatically configured address obtained via DHCP. It is usually in the form of 10.60.178.52 (although they typically end in .1 or .254 based on the scope size), and it is where your computer sends all its traffic to be routed onwards. For IPv6, there is an in-depth guide on how-to-fix-ipv6-connectivity/, but you can also check on Mac or Linux using:
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 10.60.178.52 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 fe80:505b:e4d7:3082:2fba%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): {248.210.244.84, 160.167.179.48}
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 56:7b:94:5f:ae:88
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 f0:e6:c1:f7:25:52
}
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) connection at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of the version of OSX/macOS you have, whether it’s 10.13.6, 11.5.3, or 12.2.8, there are various tools available for troubleshooting. However, manual actions and scripts do not provide a continuous set of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams that embrace remote work and Work From Anywhere (WFA).
Utilizing Pre-installed Scripts for Assistance
A useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI, and can also be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, though much of it is only relevant to wireless at a specific point in time, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz for you. To run it interactively, you can use sudo /usr/bin/sysdiagnose with 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. Keep in mind that the file sizes are approximately 300MB.
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