How Can I Understand Wifi Connectivity
The Functioning of Internet Addressing Systems
When using the internet, you are assigned a unique public IPv4 address, such as 202.149.42.172, or an IPv6 address, like 2000:abd7:d9cf:bbcd:ed44:f7b6:ec20:a599. The verification of these addresses can be done at https://test-ipv6.com/, but conveying them, especially to those less knowledgeable in technology, can be prone to error and can become complex quickly. Furthermore, this method does not provide any historical data, especially in the context of past issues.
Navigating the Internet
When accessing a webpage like https://reynolds-bechtelar.org, the initial step involves contacting a DNS server to convert the combination of the host (reynolds-bechtelar) and the Top Level Domain (org) of the URL into an IP address, such as 77.212.214.206. Additionally, your computer and browser send their type with all web requestings, such as:
Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36
The Significance of Default Gateways
Normally, your default gateway is assigned as an automatically configured address via DHCP, such as 192.0.0.229 (though they usually end in .1 or .254 depending on the scope size), and serves as the point where your computer routes all its traffic. For IPv6, a detailed guide is available at how-to-fix-ipv6-connectivity/, and you can verify this on a Mac or Linux by:
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 192.0.0.229 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 fe80:47ca:25fc:56a5:8b0b%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): {9.184.212.69, 130.83.2.211}
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 b8:f0:cf:c7:b8:e1
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 cc:41:f8:c5:e4:c3
}
Solutions for Resolving Wired and Wireless Connectivity Issues
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.
Troubleshooting Tips for Apple macOS / OSX Users
Regardless of the version of OSX/macOS you are using, whether it’s 10.13.2, 11.4.5, or 12.3.4, there are various tools available for troubleshooting. However, these manual actions and scripts fail to provide a series of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams that have adopted remote work and Work From Anywhere (WFA).
Useful Built-in Scripts for OSX/macOS
An extremely useful tool for OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless-related settings in the CLI and can also be configured to generate specific troubleshooting logs. Furthermore, the sysdiagnose tool is even more comprehensive, allowing users to generate a wide range of logs (though many are only point-in-time related to wireless, similar to wdutil).
To run the sysdiagnose tool 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 sudo /usr/bin/sysdiagnose, which will open Finder in the correct location. Just be cautious of the large file sizes, usually around 300MB.
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