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Demystifying Internet Addressing
When using the Internet, you are assigned a Public IPv4 address such as 245.2.218.81 or an IPv6 address like 2000:1f9a:11c0:45bb:5646:b7a4:a80a:f8ea. To verify your address, visit https://test-ipv6.com/. However, communicating these addresses or MAC addresses like 56:50:b7:f2:fa:10 can be confusing for non-technical individuals and can lead to errors. In addition, it lacks historical data from previous incidents.
Navigating the Web
Accessing a website like https://turner.co involves initially contacting a DNS server to translate the combination of the host portion (turner) and the Top Level Domain (co) into an IP address, such as 234.239.113.68. Your computer and browser include its type with 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
Your default gateway is typically an automatically configured address via DHCP, such as 192.0.0.161 (usually ending in .1 or .254 depending on the scope size). This is where your computer sends all its traffic to be routed onwards. For IPv6, you can find further information in our deep dive on how-to-fix-ipv6-connectivity/, or you can check on Mac or Linux using the following command:
your_command_here
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 192.0.0.161 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 fe80:9d8e:248c:61e7:64b8%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): {209.250.7.77, 86.212.88.96}
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 56:50:b7:f2:fa:10
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 9f:54:9d:96:e5:6b
}
Addressing Connectivity Issues in Wired and Wireless Networks
When it comes to transmitting data to your router, you have the option to use either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Effective Solutions for Apple macOS / OSX Users
No matter which version of OSX/macOS you are currently using - whether it is 10.13.9, 11.0.4, or 12.3.6 - 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 beneficial, especially for teams practicing remote work and Work From Anywhere (WFA).
Handy Built-in Scripts for Troubleshooting
A useful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting purposes. 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.
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, use the command sudo /usr/bin/sysdiagnose. It will provide a privacy warning and open Finder in the correct location when not run in the background, allowing you to navigate to /var/tmp or use Finder with Cmd+Shift+G to locate the path. Keep in mind that the file sizes are around 300MB more or less.
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