How To DiagnOSe Common Wifi Router Issues
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address such as 81.113.5.100 or an IPv6 address like 2000:c98e:1a20:3f04:ab7e:9648:f14:56c6. This can be verified by visiting https://test-ipv6.com/. However, explaining these addresses to individuals who are not well-versed in technology, or even referencing MAC addresses such as 40:ed:c1:d6:c1:a4, can be prone to errors and quickly become complex. Moreover, this method does not provide historical data, especially when previous issues occurred.
Navigating the World Wide Web
When you attempt to access a website, like https://upton.io, your first step is to contact a DNS server to translate the host (upton) along with the Top Level Domain (io) of the URL into an IP address, such as 172.34.96.78. Your computer and browser actually transmit this information along with all web requests, for example: Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
Understanding the Significance of Default Gateways
The default gateway is typically an address that is automatically configured via DHCP. You are assigned a default gateway, such as 10.119.61.91 (although they usually end in .1 or .254 based on the scope size), and this is where your computer directs all its traffic to be routed elsewhere. For IPv6, you can refer to our comprehensive guide on how-to-fix-ipv6-connectivity/, or use the following commands on Mac or Linux:
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 10.119.61.91 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 fe80:29f2:b86f:e522:dfb%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): {214.148.100.113, 72.223.103.144}
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 40:ed:c1:d6:c1:a4
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 8b:08:0a:78:df:ca
}
Fixing Connectivity Issues for Wired or Wireless Networks
When it comes to transmitting data to your router, you could be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of whether you are using OSX/macOS version 10.12.4, 11.1.2, or 12.1.4, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time. For this reason, automated remote troubleshooting is particularly beneficial for teams that have embraced remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts
One useful tool on OSX/macOS is the sudo wdutil info command, which displays the current wireless settings in the command line interface and can also be configured to generate specific logs for troubleshooting purposes. Alternatively, the sysdiagnose tool offers a more comprehensive option for generating a wide range of logs (albeit many are only relevant to wireless at a specific point in time, 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 (although there is minimal interaction) and it 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 or use Finder with Cmd+Shift+G to locate the path. Be mindful of the file sizes, which are approximately 300MB.
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