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Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 84.77.126.13, or an IPv6 address, like 2000:7c78:f874:89d9:5b5:a58:94a2:66f. A simple way to verify this information is through a tool like https://test-ipv6.com/. However, sharing and communicating these addresses, along with MAC addresses such as ce:f3:99:60:06:bc, can be error-prone, especially for non-technical individuals. Furthermore, it does not provide any historical data, which can be valuable when troubleshooting past issues.
Navigating the World Wide Web
Accessing a web page, such as https://brakus.name, involves reaching out to a DNS server to translate the host part (brakus) and the Top Level Domain (name) of the URL into an IP address, like 212.148.59.10. Every web request from your computer and browser includes its type and specifications, for example:
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A
Significance of Default Gateways
The default gateway, usually assigned automatically through DHCP, is an essential component of network configurations. It typically comes in the form of an address like 192.168.56.202 (although .1 or .254 are common endings depending on the scope size). This gateway serves as the centralized point where your computer forwards all its outgoing traffic. For in-depth insights on IPv6 connectivity, refer to our comprehensive guide at how-to-fix-ipv6-connectivity/. On Mac and Linux systems, you can verify this information using the following command:
ifconfig | grep 'inet6'
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 192.168.56.202 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 fe80:4ec4:72a7:b960:d4ff%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): {223.178.6.36, 231.127.16.46}
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 ce:f3:99:60:06:bc
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 22:87:a8:90:f2:0c
}
Solutions for Resolving Wired or Wireless Connectivity Issues
When it comes to sending data to your router, you may be using either a wired or a wireless (Wi-Fi) medium at the physical and data layer.
Essential Steps for Troubleshooting on Apple macOS / OSX
Regardless of whether you are using OSX/macOS versions like 10.11.5, 11.6.3, or 12.2.9, 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 crucial, especially for teams that are transitioning to remote work or adopting a Work From Anywhere (WFA) approach.
Helpful Built-in Scripts for macOS
One extremely useful tool on OSX/macOS is the sudo wdutil info command, which displays the current wireless settings in the Command Line Interface (CLI) and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can generate a wide range of logs, although many of these are only relevant at a specific point in time, similar to the wdutil tool.
To run the sysdiagnose tool in the background and generate logs in the /var/tmp/<blah>.tar.gz directory, use the command sudo nohup /usr/bin/sysdiagnose -u &. Alternatively, for interactive use, you can run sudo /usr/bin/sysdiagnose to trigger a privacy warning and access the log files. However, be mindful of the file sizes, as they typically range around 300MB.
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