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Understanding Internet Address Allocation
When connecting to the Internet, you’re assigned a public IPv4 address, such as 24.109.41.146, or an IPv6 address like 2000:6f42:fd64:cad:5993:ef54:472a:dd2b. This information can be verified at https://test-ipv6.com/. However, explaining and sharing these addresses with individuals who are not tech-savvy can be prone to errors and quickly become complex. Moreover, it lacks historical data, especially for previous issues.
Navigating the World Wide Web
When trying to access a website like https://little.com, your initial step is to contact a DNS server to convert the host part (little) along with the Top Level Domain (com) of the URL into an IP address, for example, 167.171.254.4. Furthermore, your computer and browser include its type in all web requests, such as Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
Understanding the Significance of Default Gateways
The default gateway is typically an automatically configured address through DHCP. An example of a default gateway address is 10.114.44.26 (although they usually end in .1 or .254 based on the scope size), and this is where your computer sends all its traffic to be routed onwards. For IPv6, detailed information is available on how-to-fix-ipv6-connectivity/, and you can verify it 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 10.114.44.26 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 fe80:21ea:8047:616d:eb06%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): {134.242.146.4, 233.74.247.138}
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 e0:99:94:59:a7:3b
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 82:05:99:cf:42:41
}
Resolving Issues with Wired and Wireless Connections
When dealing with data transmission at the physical and data layer, you might be using either a wired or wireless (Wi-Fi) medium to transfer the data to your router.
Effective Solutions for Apple macOS / OSX Users
No matter which version of OSX/macOS you have - whether it’s 10.11.6, 11.5.7, or 12.1.6 - 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 crucial, especially for teams that have embraced remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One incredibly helpful tool on OSX/macOS is sudo wdutil info, which provides a dump of 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 only relevant to wireless at a specific point in time, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & will execute the tool in the background and write logs to /var/tmp/<blah>.tar.gz. For an interactive run (though there isn’t much interaction), you can use sudo /usr/bin/sysdiagnose, which will display 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 typically around 300MB.
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