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Understanding Internet Addressing Mechanism
When using the Internet, individuals may be assigned a Public IPv4 address such as 168.70.89.168 or an IPv6 address such as 2000:d7e9:3d4:4f6a:5d9e:eceb:444a:c1ab. Users can verify this information by visiting https://test-ipv6.com/. However, explaining or communicating these addresses, and even mentioning MAC addresses like 1e:3b:0e:af:20:b3, can be cumbersome and prone to errors. Moreover, it does not provide historical data, particularly regarding past issues.
Navigating the World Wide Web
Accessing a website, such as https://schmitt.io, involves an initial connection to a DNS server in order to translate the host section (schmitt) and the Top Level Domain (io) of the URL into an IP address, like 137.24.110.167. When making web requests, your computer and browser also transmit their type, such as: Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
Significance of Default Gateways
The default gateway is typically an automatically assigned address through DHCP. It is usually a default gateway like 192.0.0.140 (though it often ends in .1 or .254 based on the scope size), and it serves as the router for all outgoing traffic from your computer. For IPv6, detailed instructions can be found in our article how-to-fix-ipv6-connectivity/. Alternatively, on Mac or Linux systems, you can perform the check by 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 192.0.0.140 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:bfc8:5b89:d3f8:3732%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): {11.42.231.19, 149.197.103.217}
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 1e:3b:0e:af:20: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 a3:f7:0d:85:90:ae
}
Resolving Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Steps for Troubleshooting on Apple macOS / OSX
No matter which version of OSX/macOS you are currently using, whether it’s 10.13.4, 11.2.7, or 12.1.3, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes valuable, especially for teams that are embracing remote work and the Work From Anywhere (WFA) concept.
Utilizing In-Built Scripts
One extremely useful tool on OSX/macOS is the sudo wdutil info, which provides a dump of the current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only point-in-time related to wireless, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz. For interactive use, you can run sudo /usr/bin/sysdiagnose, which will give a privacy warning and open Finder in the correct location. Alternatively, you can navigate to the /var/tmp directory or use Finder with Cmd+Shift+G to navigate to the path. Keep in mind that the file sizes are approximately 300MB.
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