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Understanding How Internet Addressing Functions
When using the Internet, individuals receive a Public IPv4 address, such as 138.180.203.251, or an IPv6 address, like 2000:1c00:1520:4106:6b1b:1e79:ca3a:9ca0. This can be verified at https://test-ipv6.com/. However, conveying these addresses to individuals who are not technologically inclined, or even stating MAC addresses such as 19:c6:01:2c:1a:b9, can lead to errors and complexity. Furthermore, this does not provide any historical data, especially from previous instances of issues.
Navigating the World Wide Web
When attempting to access a website like https://boyle.org, the first step involves contacting a DNS server to convert the host section (boyle) combined with the Top Level Domain (org) of the URL to an IP address, like 199.91.152.200. When making web requests, your computer and browser send its type, for instance: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
Understanding the Significance of Default Gateways
The default gateway is typically an automatically assigned address through DHCP. Users are provided with a default gateway, such as 192.0.0.203 (although they commonly end in .1 or .254 based on the scope size), and this is where all computer traffic is routed. For IPv6, a comprehensive analysis is available at how-to-fix-ipv6-connectivity/, and it can be verified on Mac or Linux 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 192.0.0.203 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:d978:c983:dd69:c6df%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): {218.220.87.107, 159.135.33.221}
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 19:c6:01:2c:1a:b9
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 4a:8b:9f:d7:16:95
}
Resolve 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.
Troubleshooting Solutions for Apple macOS / OSX
Regardless of whether you are using OSX/macOS versions such as 10.14.3, 11.1.2, or 12.2.3, 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 valuable, especially for teams that are embracing remote work and the Work From Anywhere (WFA) concept.
Useful Built-in Scripts
One useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can also be configured to generate specific troubleshooting logs. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant to wireless settings, similar to wdutil.
To run sysdiagnose in the background and have it write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can use the command sudo /usr/bin/sysdiagnose which will display a privacy warning. Running it in this manner should open Finder in the correct location, or you can navigate to /var/tmp using Cmd+Shift+G in Finder. It’s important to be aware of the file sizes, which are typically around 300MB.
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