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Understanding Internet Addressing
When using the Internet, you are assigned either a Public IPv4 address, such as 228.62.93.141, or an IPv6 address, such as 2000:a352:9b19:d70f:ef83:f5c7:8056:d818. You can verify this information by visiting https://test-ipv6.com/. However, it can be quite challenging for non-technical individuals to communicate these addresses or refer to MAC addresses like 62:68:1e:3b:ee:05, especially considering the lack of historical data available.
Navigating the World Wide Web
When trying to access a webpage like https://crist.io, your initial interaction is with a DNS server to convert the host domain (crist) along with the Top Level Domain (io) of the URL into an IP address, such as 6.198.192.238. Notably, your computer and browser transmit their types in all web requests, 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
Typically, your default gateway is an address automatically assigned via DHCP, like 10.42.40.255 (often ending in .1 or .254, based on the scope size), and serves as the point where your computer forwards all its traffic for routing. For more information on IPv6, an in-depth explanation is available at how-to-fix-ipv6-connectivity/. On Mac or Linux, you can verify this 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 10.42.40.255 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 fe80:87c0:26a7:86d5:d176%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): {136.228.68.207, 155.201.141.248}
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 62:68:1e:3b:ee:05
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 65:e4:f4:5c:08:a6
}
Find Solutions for Wired and Wireless Connectivity Issues
When sending data to your router, you may encounter connectivity issues at the physical and data layer, whether you are using a wired or wireless (Wi-Fi) medium.
Troubleshooting Tips for Apple macOS / OSX Users
Regardless of the version of OSX/macOS you are using, such as 10.12.3, 11.1.6, or 12.0.2, there are various tools available for troubleshooting. However, manual actions and scripts may not provide a series of correlated values over time. This is where automated remote troubleshooting becomes valuable, especially for teams that embrace remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One useful tool for OSX/macOS users 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. Another comprehensive tool is the sysdiagnose tool, which can generate a wide range of logs, although much of it is point-in-time related to wireless, 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 &. For interactive use, you can run sudo /usr/bin/sysdiagnose and follow the privacy warning. When not run in the background, it will open Finder in the correct location, or you can navigate to /var/tmp using Finder with Cmd+Shift+G. Be aware that the file sizes are approximately 300MB.
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