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Understanding Internet Addressing
When you connect to the Internet, your device is assigned a public IP address, such as 43.211.139.119 for IPv4 or 2000:6c3c:a8f:3ede:d12e:585a:6e01:a4bc for IPv6. You can verify this by visiting https://test-ipv6.com/. However, explaining these addresses, including MAC addresses like f4:25:3e:5a:db:b3, to those who are not familiar with technology can be complex and error-prone. Furthermore, this method does not provide historical data, especially for past issues.
Navigating the World Wide Web
When you want to visit a website like https://parisian-heidenreich.net, your computer first accesses a DNS server to translate the URL’s host (parisian-heidenreich) and Top Level Domain (net) to an IP address, such as 86.102.249.70. Additionally, your computer and browser specify their type with every web request, for example: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36
The Significance of Default Gateways
By default, your gateway is assigned automatically through DHCP, often with an address like 192.168.222.11 (typically ending in .1 or .254 based on the scope size). This is the location where your computer forwards all its traffic to be routed. For IPv6, you can delve deeper into the topic by visiting how-to-fix-ipv6-connectivity/ or check on Mac or Linux using the following command:
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 192.168.222.11 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 fe80:37f3:1ac4:705d:bc86%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): {197.220.11.19, 16.104.40.39}
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 f4:25:3e:5a:db:b3
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 47:9e:7d:b8:97:f7
}
Fixing Connectivity Issues: Wired vs. Wireless
Whether you are using a wired or wireless (Wi-Fi) medium to transmit data to your router, issues can arise at the physical and data layers.
Troubleshooting Techniques for Apple macOS / OSX
No matter which version of OSX/macOS you are currently running - whether it’s 10.12.8, 11.0.3, or 12.2.4, there is a variety of tools available for troubleshooting. However, the manual actions and scripts fall short in providing a series of correlated values over time. This is where automated remote troubleshooting becomes essential, particularly for teams that are embracing remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One extremely helpful tool on OSX/macOS is the sudo wdutil info command, which provides a dump to the CLI of current wireless settings, and can also be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a comprehensive range of logs, even though much of it is only point-in-time data in relation to wireless, similar to wdutil.
To run sysdiagnose in the background and generate logs in /var/tmp/<blah>.tar.gz, you can use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, use the command sudo /usr/bin/sysdiagnose, but be aware of the large file size of about 300MB.
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