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Understanding Internet Addressing
When using the Internet, you may be assigned a Public IPv4 address such as 206.231.244.210 or an IPv6 address like 2000:24f0:39cd:661:8dfa:f6cb:1736:ac7d. You can verify this by visiting https://test-ipv6.com/. However, conveying these addresses or MAC addresses like 11:a2:bf:38:2d:a5 to individuals who are not technologically inclined can be prone to errors and can quickly become complex. Moreover, this does not provide any historical data, especially for past issues.
Navigating the World Wide Web
When attempting to access a web page such as https://rippin.org, your first step is to contact a DNS server to convert the host portion (rippin) combined with the Top Level Domain (org) of the URL into an IP address such as 166.70.226.153. Your computer and browser transmits its type with every web request, for example: Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0.
The Significance of Default Gateways
Your default gateway is typically assigned automatically through DHCP. It is usually an address like 10.152.99.253 (although they typically end in .1 or .254 depending on the scale) and it is responsible for routing all of your computer’s traffic. For IPv6, detailed instructions can be found in our article how-to-fix-ipv6-connectivity/. Alternatively, on Mac or Linux, you can check with 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 10.152.99.253 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 fe80:89c8:3baa:def3:d189%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): {98.139.125.102, 16.103.165.224}
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 11:a2:bf:38:2d:a5
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 85:0f:89:bb:9b:dd
}
Troubleshooting Network Connectivity
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.
Resolving Issues on Apple Devices
No matter which version of macOS or OSX you are currently using - whether it’s 10.15.9, 11.3.5, or 12.3.5 - there are a variety of troubleshooting tools available. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes essential, especially for teams that embrace remote work and Work From Anywhere (WFA).
Utilizing Built-in Tools for Assistance
A useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to produce a wide range of logs, although much of it is only relevant to wireless at a specific point in time, similar to wdutil.
Running the command sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz for you. Alternatively, you can run sudo /usr/bin/sysdiagnose interactively, which 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 or use Finder with Cmd+Shift+G to locate the file. Keep in mind that the file sizes are approximately 300MB.
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