How Can I Troubleshoot OSX Internet Connection
Understanding the Functioning of Internet Addressing
When using the Internet, you are assigned either a Public IPv4 address such as 165.125.243.124 or an IPv6 address like 2000:8aa7:93bc:1164:6d70:bdf8:ea2f:dfa6. These can be verified by visiting https://test-ipv6.com/. However, for individuals who are not well-versed in technology, relaying or referencing these addresses, or even identifying MAC addresses like 52:f4:8d:9e:44:46, can be prone to errors and quickly become complex. Furthermore, this does not provide any historical data, particularly regarding past issues.
Navigating the World Wide Web
In order to access a website like https://lynch-kovacek.net, initial contact is made with a DNS server to convert the host part (lynch-kovacek) in conjunction with the Top Level Domain (net) of the URL, into an IP address like 172.0.39.255. With every web request, your computer and browser actually disclose their type, for exampleMozilla/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 usually an address that is automatically configured through DHCP. Usually, you are given a default gateway similar to 192.0.0.75 (usually ending in .1 or .254 depending on the scope size), and this is where your computer directs all its traffic to be routed further. To delve deeper into IPv6, you can refer to how-to-fix-ipv6-connectivity/ or check on Mac or Linux with:
command to check the default gateway
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 192.0.0.75 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 fe80:1f61:6995:5807:226b%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): {98.84.251.82, 19.205.18.221}
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 52:f4:8d:9e:44:46
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 77:5f:05:0d:5a:c9
}
Solutions for Wired and Wireless Connectivity Issues
When it comes to transmitting data to your router, you may be using either a wired or wireless (Wi-Fi) connection at the physical and data layer.
How to Address Problems on Apple macOS / OSX
No matter the version of OSX/macOS you are currently using, whether it’s 10.11.5, 11.5.6, or 12.3.3, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes particularly useful, especially for teams that embrace remote work and Work From Anywhere (WFA).
Useful Built-in Scripts for Troubleshooting
One extremely valuable 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 purposes. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant to wireless information, similar to wdutil.
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can use the command sudo /usr/bin/sysdiagnose (although there is not much interaction) and it will provide 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. Keep in mind that the file sizes are approximately 300MB.
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