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The Fundamentals of Internet Addressing
When using the Internet, you will be assigned either a Public IPv4 address, such as 49.149.58.162, or an IPv6 address, such as 2000:a3ee:42df:b498:58b1:2dad:950b:c284. You can verify this at https://test-ipv6.com/. However, for those who are not well-versed in technology, conveying and working with these addresses, or even referencing MAC addresses like fc:3c:d8:e2:c7:28, can be prone to errors and become complex very quickly. Furthermore, this method does not provide any historical data, especially when addressing past issues.
Navigating the World Wide Web
When attempting to access a webpage, such as https://torp.name, the first step is connecting to a DNS server to translate the host portion (torp) in conjunction with the Top Level Domain (name) of the URL into an IP address like 139.48.249.218. Each web request from your computer and browser includes details about its type, for example: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
Understanding the Significance of Default Gateways
Your default gateway is typically an address that is configured automatically through DHCP. This gateway address, such as 10.60.229.70 (although it usually ends in .1 or .254, depending on the scope size), is where your computer routes all its traffic. For a comprehensive insight into IPv6, refer to how-to-fix-ipv6-connectivity/. You can also verify this on Mac or Linux by 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 10.60.229.70 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 fe80:4c83:b1a0:246e:e080%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): {79.221.161.112, 163.176.229.167}
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 fc:3c:d8:e2:c7:28
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 be:81:e5:02:c4:05
}
Resolving Issues with Wired and Wireless Connections
When it comes to transferring data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of the version of OSX/macOS you are using, whether it’s 10.11.8, 11.0.5, or 12.0.3, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes essential, particularly for teams that are focused on remote work and Work From Anywhere (WFA).
Effective Built-in Scripts
One useful tool on OSX/macOS is the sudo wdutil info, which provides a dump of current wireless settings to the CLI and can be configured to generate specific troubleshooting logs. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs, although many of them are only relevant to a specific 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. If you prefer to run it interactively, you can use sudo /usr/bin/sysdiagnose and it will prompt a privacy warning. When not run in the background, it should open Finder in the correct location or you can navigate to /var/tmp using Finder with Cmd+Shift+G. However, be cautious of the file sizes, which are around 300MB more or less.
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