Troubleshoot Common Wifi Connectivity
Understanding the Function of Internet Addressing
When using the Internet, your device may be assigned a Public IPv4 address, such as 205.155.44.73, or an IPv6 address, like 2000:b2ac:d947:2a8a:cca3:8fb:cdf3:582f. These addresses can be verified at https://test-ipv6.com/, but conveying them in a comprehensible manner to non-experts can be complicated and prone to errors. Moreover, historical data is not available, especially for past issues.
Navigating to Websites
In order to access a website like https://jast.name, the initial step involves contacting a DNS server to convert the combination of the host portion (jast) and the Top Level Domain (name) of the URL into an IP address, such as 147.144.10.115. Additionally, your computer and browser transmit their specifications with every web request, for example, 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
The default gateway is typically assigned automatically through DHCP and may take the form of an address like 192.168.185.224 (usually ending in .1 or .254 based on the scope size). This is where your computer directs all its traffic for further routing. While instructions for checking on Mac or Linux can be found at how-to-fix-ipv6-connectivity/, a deep dive into IPv6 connectivity is available as well.
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 192.168.185.224 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:ad7e:e5a4:caff:4560%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): {36.157.235.129, 182.81.94.93}
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 81:17:86:cf:df: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 98:9f:82:b9:31:77
}
Resolve Issues with Wired and Wireless Connections
When sending data to your router, you may encounter connection issues at the physical and data layer, whether you are using a wired or wireless (Wi-Fi) medium.
Troubleshooting Tips for Apple macOS/OSX
Regardless of your version of OSX/macOS, be it 10.15.1, 11.0.7, or 12.2.1, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams engaged in remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One particularly helpful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can generate a wide range of logs, but much of it is only related to wireless settings at a specific point in time, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz. For an interactive experience (though there is minimal interaction), you can run sudo /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 using Cmd+Shift+G in Finder. However, be mindful of large file sizes, typically around 300MB.
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