How To Troubleshoot MacOS Connectivity
Explanation of Internet Addressing Mechanism
When using the Internet, individuals may have a unique Public IPv4 address such as 117.215.73.46 or the newer IPv6 address format like 2000:d1e6:e89a:fee:5da4:879:a873:7a9f. Verification of these addresses can be done at https://test-ipv6.com/. However, explicating these addresses and even referencing MAC addresses such as e7:7a:83:ed:b1:df can become complex and prone to errors. Moreover, it fails to provide any historical data, particularly related to previous issues encountered.
Navigating the World Wide Web
Accessing a website like https://lebsack-klocko.co initially requires communication with a DNS server to convert the host portion (lebsack-klocko) combined with the Top Level Domain (co) of the URL to an IP address, for example, 140.173.168.215. When communicating with web servers, your computer and browser also transmit specific data such as Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0.
Significance of Default Gateways
The default gateway is typically an automatically assigned address through DHCP. An example of a default gateway could be 10.144.161.36 (although they generally end in .1 or .254 based on size). This is where all the traffic from your computer is directed for further routing. For IPv6, a detailed guide on this topic is available at how-to-fix-ipv6-connectivity/, and verification on Mac or Linux can be done 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 10.144.161.36 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 fe80:43d5:4342:a02e:9b59%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): {71.144.20.190, 9.172.172.189}
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 e7:7a:83:ed:b1:df
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 2d:66:6e:ae:12:03
}
How to Troubleshoot Network Issues
When it comes to troubleshooting network issues, whether using a wired or wireless connection, it is important to understand the tools and methods available at the physical and data layer.
Tips for Troubleshooting on Apple Devices
No matter which version of the Apple operating system you are running, such as 10.11.8, 11.5.8, or 12.1.9, there are various techniques for troubleshooting network problems. However, these manual methods and scripts may not provide a continuous stream of relevant data over time. This is where automated remote troubleshooting becomes valuable, particularly for teams working remotely or embracing a “Work From Anywhere” (WFA) approach.
Using Built-in Tools for Network Diagnostics
On OSX/macOS, the sudo wdutil info command can provide a detailed dump of current wireless settings through the command line interface. It can also be configured to generate specific logs for troubleshooting purposes. In addition, the sysdiagnose tool offers a comprehensive range of logs, although many of them are only point-in-time data in relation to wireless, similar to wdutil.
Run sudo nohup /usr/bin/sysdiagnose -u & in the background to generate logs in /var/tmp/<blah>.tar.gz. For interactive use (although it is not very interactive), run sudo /usr/bin/sysdiagnose and follow the privacy warning. If not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp using Cmd+Shift+G in Finder. Keep in mind that the file size is approximately 300MB.
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