DiagnOSe OSX Internet Connection
The Functioning of Internet Addressing
When connecting to the Internet, one might receive a Public IPv4 address, such as 234.134.240.159, or an IPv6 address, such as 2000:70d4:f0ae:7955:21b0:9e65:c0af:2ad4. These addresses can be verified by visiting https://test-ipv6.com/. However, for individuals who are not proficient in technology, attempting to convey these addresses, or even mentioning MAC addresses like 2a:9c:5b:19:ff:95, can be prone to errors and become complex rapidly. Moreover, this method does not provide any historical data, particularly from previous instances when problems occurred.
Navigating the Internet
To access a webpage, such as https://wunsch.com, one first interacts with a DNS server to convert the host section (wunsch) coupled with the Top Level Domain (com) of the URL into an IP address, such as 215.2.127.158. The computer and browser actually transmit their type with all web requests, for example: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
The Significance of Default Gateways
The default gateway is typically an automatically configured address via DHCP. It provides a default gateway such as 192.0.0.146 (although they usually end in .1 or .254 based on the scope size) and this is where the computer dispatches all of its traffic to be routed onward. For IPv6, a detailed examination can be found on how-to-fix-ipv6-connectivity/, but it can also be verified on Mac or Linux with:
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 192.0.0.146 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:d6ac:5fa1:840e:31fc%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): {130.170.13.38, 79.250.95.169}
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 2a:9c:5b:19:ff:95
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 f4:af:3e:a0:d8:3e
}
Troubleshooting Connectivity Issues
When it comes to transferring data to your router, you might be using either wired or wireless (Wi-Fi) connections at the physical and data layer.
Steps for Apple macOS / OSX Users
Regardless of which version of OSX/macOS you are using - whether it’s 10.15.1, 11.4.7, or 12.2.3 - there are various troubleshooting tools available. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes valuable, particularly for teams that embrace remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts
One useful tool for OSX/macOS users is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can also generate specific troubleshooting logs. Moreover, the sysdiagnose tool offers a more comprehensive range of logs, although much of it is specific to wireless and only captures point-in-time data like wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will generate logs in /var/tmp/<blah>.tar.gz. If you prefer to run it interactively, you can execute sudo /usr/bin/sysdiagnose, which will prompt a privacy warning. When not run in the background, it will open Finder in the correct location or you can navigate to /var/tmp or use Finder with Cmd+Shift+G to find the path. However, be mindful of the file sizes, which are approximately 300MB.
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