How Can I Troubleshoot Common Wifi Router Issues
Understanding Internet Address Structure
When using the Internet, you may be assigned a Public IPv4 address, such as 208.190.111.163, or an IPv6 address, such as 2000:dd9f:be77:56db:90b:845:74aa:5b. This information can be verified at https://test-ipv6.com/. However, conveying these addresses to non-technical individuals, or even mentioning MAC addresses like 24:9d:3e:47:0b:7d, can lead to errors and complexity. Moreover, it does not provide historical data, especially regarding past issues.
Navigating the World Wide Web
When accessing a website, such as https://kuhn.com, your computer initially connects to a DNS server to convert the host part (kuhn) combined with the Top Level Domain (com) of the URL into an IP address, like 43.239.104.104. With each web request, your computer and browser also transmit their type, for example,
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
The default gateway is usually an address automatically assigned through DHCP. Examples include 172.21.56.163 (often ending in .1 or .254 depending on the scope size) to which your computer forwards all traffic. For IPv6, detailed guidance is available at how-to-fix-ipv6-connectivity/, but for Mac or Linux, verification can be done using:
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 172.21.56.163 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:c902:a3a2:939:373e%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): {125.31.51.241, 117.18.215.127}
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 24:9d:3e:47:0b:7d
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 13:f0:54:db:80:3c
}
Dealing with Wired and Wireless Issues
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
No matter which version of OSX/macOS you are currently using - whether it’s 10.15.6, 11.2.1, or 12.0.1 - there are various tools available for troubleshooting issues. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes especially valuable, particularly for teams that embrace remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
An incredibly helpful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI and can also be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant at a specific point in time in relation to wireless, similar to wdutil.
To run sysdiagnose in the background and have it write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. On the other hand, if you prefer to run it interactively, use the command sudo /usr/bin/sysdiagnose - although it 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 Finder with Cmd+Shift+G to locate the path. Keep in mind that the file sizes are approximately 300MB.
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