How To DiagnOSe Common Wifi Issues
Understanding How Internet Addresses Function
When using the Internet, you will have either a Public IPv4 address (like 46.214.126.203) or an IPv6 address (like 2000:658b:ee1b:6e51:7614:4ad2:835b:19ff). You can verify this at https://test-ipv6.com/. However, for those not well-versed in technology, attempting to communicate these addresses, or even recite MAC addresses (like 15:39:6c:d6:2e:d1), can be prone to errors and become complex. Moreover, this method does not provide any historical data, especially with regards to past issues.
Navigating the Internet
When accessing a website such as https://nicolas.net, you initially connect to a DNS server to convert the combination of the host portion (nicolas) and the Top Level Domain (net) of the URL into an IP address, such as 207.94.206.237. When making any web requests, your computer and browser transmit the data type, as seen in the example below:
Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)
Understanding the Significance of Default Gateways
Typically, your default gateway address is configured automatically by DHCP. You will receive a default gateway address (like 192.168.108.235, often ending in .1 or .254 depending on the scope size), and this is where your computer directs all its traffic for further routing. For a more in-depth look into IPv6 connectivity issues, refer to our article how-to-fix-ipv6-connectivity/, or perform checks on Mac or Linux using the method shown below:
<br>
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 192.168.108.235 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 fe80:38b5:740e:3c53:edb%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): {107.90.41.92, 186.18.27.48}
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 15:39:6c:d6:2e:d1
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 32:c7:77:cd:10:cb
}
Resolving Issues with Wired and Wireless Connections
When it comes to transmitting data at the physical and data layer, you may opt for a wired or wireless (Wi-Fi) medium to connect to your router.
Solutions for Apple macOS / OSX Users
Regardless of whether you are using OSX/macOS versions such as 10.11.1, 11.3.5, or 12.1.5, there are several troubleshooting tools available. Unfortunately, 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).
Utilizing Built-in Scripts
A useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless related settings to the CLI. This can also be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool offers a more comprehensive approach, generating a wide range of logs related to wireless (though much of it is point-in-time only, similar to wdutil).
To run sysdiagnose in the background and generate logs in /var/tmp/<blah>.tar.gz, you can use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can use the command sudo /usr/bin/sysdiagnose which will issue 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 the file sizes, which are approximately 300MB or slightly more.
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