How To DiagnOSe Common Wifi Connectivity
Understanding Internet Addressing
When you connect to the Internet, you are assigned a unique public IPv4 or IPv6 address. This can be verified on https://test-ipv6.com/. However, for those who are not familiar with technical aspects, communicating or referencing these addresses, as well as MAC addresses like 9c:0d:24:08:6c:b7, can be error-prone and complex. Furthermore, this method lacks historical data, especially when issues have occurred in the past.
Navigating the World Wide Web
To access a website such as https://toy.org, your computer initially communicates with a DNS server to convert the host name (toy) and the Top Level Domain (org) of the URL into an IP address, such as 126.10.153.227. Every web request actually includes the type of your computer and browser, for example: Mozilla/5.0 (Windows; U; Win 9x 4.90; SG; rv:1.9.2.4) Gecko/20101104 Netscape/9.1.0285
The Significance of Default Gateways
Your default gateway is typically automatically configured through DHCP and is assigned an address like 10.45.105.87 (although they typically end in .1 or .254, depending on the scope size). This is the destination where your computer sends all its traffic to be routed onwards. For troubleshooting IPv6 connectivity on Mac or Linux, you can refer to our in-depth guide at how-to-fix-ipv6-connectivity/.
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 10.45.105.87 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 fe80:8c3e:c448:9eea:8475%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): {0.93.227.33, 209.212.218.37}
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 9c:0d:24:08:6c:b7
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 a1:b6:a0:1e:01:89
}
Resolving Wired vs. Wireless Issues
When transmitting data to your router, you might be utilizing a wired or wireless (Wi-Fi) connection at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of the version of OSX/macOS you are using, whether it’s 10.13.9, 11.4.7, or 12.0.4, 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, especially for teams that are embracing remote work and Work From Anywhere (WFA).
Helpful Built-in Scripts
One very useful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI, and it can also be configured to generate specific troubleshooting logs. In addition, the sysdiagnose tool offers a more comprehensive option for generating a wide range of logs, although many are only point-in-time logs 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 &. If you prefer to run it interactively, use sudo /usr/bin/sysdiagnose, but be cautious of the large file sizes of about 300MB.
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