DiagnOSe Common Wifi No Access
Understanding Internet Addressing
When using the Internet, one might encounter a Public IPv4 address such as 188.42.106.108 or an IPv6 address like 2000:2d7d:a76:8ceb:4258:c8b5:20ed:632e. This information can be verified using https://test-ipv6.com/. However, relaying these addresses to individuals who are not well-versed in technology, or even mentioning MAC addresses like fb:af:df:23:60:ed, can be prone to errors and can become complex very quickly. Moreover, this does not provide any historical data, especially when problems were experienced in the past.
Navigating the Web
In order to access a webpage such as https://walker-waelchi.biz, the user initially contacts a DNS server to convert the host part (walker-waelchi) combined with the Top Level Domain (biz) of the URL to an IP address, such as 199.15.194.245. Interestingly, the user’s computer and browser sends its type with every web request, such as Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
The Significance of Default Gateways
The default gateway is typically an address that is automatically configured via DHCP. An example of a default gateway may be 172.20.47.10 (although they often end in .1 or .254 depending on the scope size), and this is where a user’s computer sends all its traffic to be routed onwards. For IPv6, a detailed guide can be found on how-to-fix-ipv6-connectivity/, but it can be checked 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 172.20.47.10 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 fe80:2785:64a2:daad:c5a3%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): {207.224.114.249, 127.95.133.146}
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 fb:af:df:23:60:ed
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 70:b3:67:bb:77:86
}
Resolve Issues with Wired and Wireless Connections
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
Regardless of the version of OSX/macOS you’re using, whether it’s 10.15.6, 11.6.9, or 12.2.4, there are various tools available for resolving issues. 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 remote work teams and those following a Work From Anywhere (WFA) approach.
Useful Built-in Scripts
On OSX/macOS, the sudo wdutil info tool is quite valuable as it provides a CLI dump of current wireless settings and can be configured to generate specific troubleshooting logs. In addition, the sysdiagnose tool can generate a wide range of logs, although many are only relevant to wireless networks, just like wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively, you can run sudo /usr/bin/sysdiagnose, which will give a privacy warning. When not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp using Finder with Cmd+Shift+G. However, be mindful of file sizes, which are typically around 300MB.
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P.S. Tips For Remote Network and Client Support
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