How To Check OSX Internet Connection
Understanding Internet Address Assignment
When you are using the internet, you will receive a Public IPv4 address, such as 87.126.190.195, or an IPv6 address, like 2000:361e:b340:a818:ee30:c337:b008:9645. These addresses can be verified by visiting https://test-ipv6.com/. However, relaying these addresses, as well as MAC addresses like a0:b2:c5:32:28:76, to individuals who are not tech-savvy can be prone to errors and quickly become complex. Moreover, this method does not provide any historical data, especially when dealing with past issues.
Navigating the World Wide Web
When attempting to access a webpage, such as https://christiansen.org, the first step involves connecting to a DNS server to convert the host portion (christiansen) and the Top Level Domain (org) of the URL into an IP address, like 215.17.11.39. Moreover, every web request sent by your computer and browser includes its type, for example: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko.
The Significance of Default Gateways
Your default gateway is typically automatically assigned via DHCP and appears as an address such as 192.0.0.241 (although they usually end in .1 or .254 depending on the scope size). This is the point where your computer directs all its traffic to be routed to. A more detailed discussion on IPv6 is available at how-to-fix-ipv6-connectivity/, and you can verify this 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 192.0.0.241 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 fe80:8711:e097:84f0:5f8f%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): {79.160.139.12, 172.6.20.210}
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 a0:b2:c5:32:28:76
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 87:72:16:4d:27:26
}
Resolve Wired and Wireless Connectivity Issues
When it comes to transmitting data to your router, you may find yourself using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX Users
Regardless of whether you are running OSX/macOS versions such as 10.14.7, 11.0.7, or 12.3.8, there are various troubleshooting tools available. However, manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes invaluable, particularly for teams that are embracing remote work and the Work From Anywhere (WFA) concept.
Useful Built-in Scripts
A highly beneficial tool on OSX/macOS is sudo wdutil info, 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 offers a more comprehensive option for generating a wide range of logs, although much of it is only relevant to wireless in a point-in-time context, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will generate logs in /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (even though there is minimal interaction), you can execute sudo /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 Finder with Cmd+Shift+G. However, be cautious of the file sizes, which can be around 300MB or more.
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