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Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address such as 249.129.105.76 or an IPv6 address like 2000:f781:4c9f:8c08:fb8:3b33:1a9d:3aea. Verifying these addresses is possible by visiting https://test-ipv6.com/. However, conveying these addresses to individuals who are not tech-savvy, or even sharing MAC addresses like c5:d8:b7:44:42:23, can lead to errors and complexity. Additionally, this method does not provide any historical data, especially related to past issues.
Navigating the World Wide Web
When attempting to access a webpage, such as https://keebler.co, your first step is to contact a DNS server to translate the host portion (keebler) combined with the Top Level Domain (co) of the URL into an IP address, for example 15.86.203.118. When making web requests, your computer and browser include detailed information such as:
Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36
Understanding Default Gateways
The default gateway is typically an address that is automatically configured through DHCP. This gateway, such as 10.212.234.170 (often ending in .1 or .254 depending on the scope size), serves as the destination for all of your computer’s outgoing traffic. For those keen to learn more about IPv6, further information can be found in our detailed exploration at how-to-fix-ipv6-connectivity/. Additionally, testing on Mac or Linux systems can be done 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 10.212.234.170 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:c8a6:ac77:9bd8:e85d%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): {42.203.161.12, 216.142.29.25}
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 c5:d8:b7:44:42:23
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 69:b1:9a:b4:89:54
}
Resolving Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting on Apple macOS / OSX
Regardless of whether you are using OSX/macOS versions such as 10.12.2, 11.2.8, or 12.1.5, there are various troubleshooting tools available. However, manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting proves to be particularly valuable, especially for teams that are embracing remote work and Work From Anywhere (WFA).
Effective Built-in Scripts
On OSX/macOS, a very useful tool is sudo wdutil info, which provides a dump of the current wireless settings to the CLI and can also 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 related to wireless on a point-in-time basis just like wdutil.
You can run sudo nohup /usr/bin/sysdiagnose -u & in the background, and it will write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (even though there isn’t much interaction), you can runsudo /usr/bin/sysdiagnose and a privacy warning will appear. When not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp or use Finder with Cmd+Shift+G to point Finder to the path. Just be aware that the file sizes are approximately 300MB or thereabouts.
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