How To DiagnOSe Wifi No Access
Understanding Internet Addressing Systems
When using the Internet, individuals may have a Public IPv4 address, such as 37.19.55.220, or an IPv6 address, such as 2000:a1e7:3b65:c4a6:37b:3dd0:87c3:77aa. Verification of these addresses can be done using https://test-ipv6.com/, but conveying these addresses and MAC addresses like aa:17:f2:a8:d6:3d to those who are not technically inclined can be prone to errors and rapidly become complex. Furthermore, this method does not provide any historical information, which would be particularly useful for resolving past issues.
Navigating the Internet
In order to reach a web page, for example, https://cartwright.name, the DNS server must initially translate the host portion (cartwright) combined with the Top Level Domain (name) of the URL to an IP address, such as 210.155.235.165. Every web request that is sent from your computer and browser contains important information about the type of browser being used, for example: Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
The Significance of Default Gateways
Usually, the default gateway is an address that is configured automatically via DHCP, for example 192.0.0.137 (although they usually end in .1 or .254 depending upon the scope size). This is the point to which your computer sends all of its traffic to be routed onwards. A detailed guide on how to fix IPv6 connectivity can be found here, or alternatively, you can check on Mac or Linux with:
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 192.0.0.137 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 fe80:5aaa:2d51:f147:4e20%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): {235.192.175.91, 250.41.157.101}
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 aa:17:f2:a8:d6:3d
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 a4:a7:bd:6f:cc:12
}
Fixing Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you can do so using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Steps to Take on Apple macOS / OSX
Regardless of whether you are using OSX/macOS version 10.15.1, 11.1.6, or 12.3.1, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes valuable, particularly for teams that embrace remote work and Work From Anywhere (WFA).
Pre-installed Scripts for Assistance
One useful tool on OSX/macOS is the sudo wdutil info, which provides a dump to the CLI of current wireless related settings and can be configured to generate specific logs for troubleshooting. Additionally, the more comprehensive sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant to wireless issues, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & will execute it in the background and write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (although there is not much interaction), you can executesudo /usr/bin/sysdiagnose, which will prompt a privacy warning. When not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp or use Finder with Cmd+Shift+G to direct Finder to the path. Keep in mind that the file sizes are approximately 300MB.
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