How To DiagnOSe MacOS Connectivity
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 180.82.215.125, or an IPv6 address, like 2000:1a3e:c04e:bed5:dba3:27c3:6ed5:dd61. Verification of your IP address can be done at https://test-ipv6.com/, but translating these addresses, as well as MAC addresses like 69:69:64:fe:24:a7, can be challenging for non-technical individuals. Moreover, this method does not provide any historical data, especially for previous issues encountered.
Navigating the World Wide Web
When attempting to visit a webpage, such as https://zemlak.io, you must first access a DNS server to convert the URL’s host portion (zemlak) combined with the Top Level Domain (io) into a corresponding IP address, like 89.245.152.69. It is important to note that your computer and browser disclose their type with every web request, for example:
Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
Significance of Default Gateways
The default gateway, generally acquired through DHCP, is an automatically configured address. Usually, the default gateway is designated as 192.0.0.247 (often ending in .1 or .254 based on scope size), and it serves as the point where your computer forwards all its traffic for routing. While a detailed explanation of IPv6 connectivity can be found at how-to-fix-ipv6-connectivity/, you can verify it on Mac or Linux by:
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 192.0.0.247 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 fe80:5f32:8a38:d4da:b49b%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): {80.127.131.126, 152.222.79.91}
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 69:69:64:fe:24:a7
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 dd:27:cc:d9:5d:2d
}
Resolve Wired or Wireless Connectivity Issues
When it comes to transferring data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
How to Address Connectivity Problems on Apple macOS / OSX
Regardless of whether you are running OSX/macOS versions such as 10.13.7, 11.5.5, 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, which is where automated remote troubleshooting becomes invaluable, especially for teams embracing remote work and Work From Anywhere (WFA).
Helpful Built-in Scripts
One useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings in the CLI and can be configured to generate specific troubleshooting logs. Furthermore, the sysdiagnose tool offers a more comprehensive option for generating a wide range of logs, although many are only relevant to the wireless connection 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. If you prefer to run it interactively (although there is minimal interaction), you can execute
sudo /usr/bin/sysdiagnose and it 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 or use Finder with Cmd+Shift+G to specify the path. Keep in mind that the file sizes are approximately 300MB.
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