How To Understand Common Wifi No Access
Explanation of Internet Addressing
When using the Internet, you are assigned a public IP address, such as 125.86.198.26 for IPv4 or 2000:a99:19cf:dbb5:8363:2c7c:3a04:89ae for IPv6. To verify your IP address, you can visit https://test-ipv6.com/. However, conveying these addresses, as well as MAC addresses like 4b:db:6f:32:5f:38, to those who are not tech-savvy can be prone to errors and become complex. Moreover, this method does not provide any historical data, particularly when dealing with past issues.
Navigating the World Wide Web
In order to reach a website, such as https://deckow.net, you initially contact a DNS server to convert the URL’s host segment (deckow) along with its Top Level Domain (net) into an IP address, such as 179.239.136.154. Additionally, your computer and browser transmit their types with all web requests, for example: Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
Understanding the Significance of Default Gateways
Usually, your default gateway is automatically assigned through DHCP and typically appears as 192.168.245.193 (commonly ending in .1 or .254, based on the scope size). This is where your computer forwards all its traffic to be routed further. For IPv6, you can have a detailed understanding by referring to how-to-fix-ipv6-connectivity/, or you can verify on Mac or Linux using the following command:
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 192.168.245.193 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:e5fd:b772:7cd8:784b%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): {197.213.76.112, 234.204.124.157}
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 4b:db:6f:32:5f:38
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 18:e4:c7:1c:cd:96
}
Solutions for Resolving Wired or Wireless Issues
When it comes to sending data to your router, you may encounter issues at the physical and data layer, whether you are using a wired or wireless (Wi-Fi) medium.
Tips for Troubleshooting on Apple macOS / OSX
Regardless of the version of OSX/macOS you are using, such as 10.13.6, 11.4.4, or 12.2.6, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes valuable, particularly for teams that practice remote work and Work From Anywhere (WFA).
Effective Built-in Tools for Assistance
One useful tool on OSX/macOS is the sudo wdutil info, which provides a dump of current wireless settings in the CLI and can be configured to generate specific logs for troubleshooting. Another comprehensive tool is the sysdiagnose, which can 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 sudo nohup /usr/bin/sysdiagnose -u & in the background and write logs to /var/tmp/<blah>.tar.gz. To run it interactively, you can use sudo /usr/bin/sysdiagnose and it will give a privacy warning. When not running in the background, it should open Finder in the correct location, or you can navigate to /var/tmp using Finder with Cmd+Shift+G. Keep in mind that the file sizes are approximately 300MB.
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