How To DiagnOSe Wifi Router Issues
Demystifying Internet Addressing
When you connect to the Internet, your device is assigned a Public IPv4 address, such as 47.16.126.239, or an IPv6 address, such as 68:a7:7933:dc85:43ae:f8cf:c8fc:b7e6. You can verify these addresses by visiting https://test-ipv6.com/. However, when it comes to communicating these addresses or MAC addresses, such as db:a0:27:97:87:c3, with individuals who are not tech-savvy, it can quickly become complicated and error-prone. Additionally, this method does not provide any historical data of previous issues.
Navigating the World Wide Web
In order to access a website, like https://hermann-veum.info, your device initially contacts a DNS server to translate the host portion (hermann-veum) combined with the Top Level Domain (info) of the URL into an IP address, such as 146.199.23.163. When making web requests, your computer and browser also send information about their type, for example: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko.
Understanding the Significance of Default Gateways
Your default gateway is typically automatically configured through DHCP and is usually assigned an address, such as 192.168.132.117 (although they often end in .1 or .254, depending on the scope size). This is the point to which your computer sends all of its traffic to be routed onwards. For an in-depth understanding of the default gateway for IPv6, you can refer to how-to-fix-ipv6-connectivity/. On Mac or Linux, you can verify this information by:
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 192.168.132.117 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 fe80:1906:3949:c737:4f58%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): {3.120.75.136, 169.68.134.220}
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 db:a0:27:97:87:c3
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 ce:95:53:3a:43:8c
}
Resolving Connection Issues for Wired and Wireless Networks
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 Solutions for Apple macOS / OSX
Regardless of whether you’re running OSX or macOS versions like 10.13.2, 11.4.4, or 12.2.9, there are various troubleshooting tools available. While manual actions and scripts can be helpful, they don’t provide a series of correlated values over time. This is where automated remote troubleshooting becomes valuable, especially for teams that adopt remote work and Work From Anywhere (WFA).
Embedded Tools for Assistance
An extremely useful 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. Moreover, the sysdiagnose tool offers a more comprehensive option, generating a wide range of logs (although many are only relevant to wireless at a specific moment, similar to wdutil).
By running sudo nohup /usr/bin/sysdiagnose -u &, the tool will run in the background and write logs to /var/tmp/<blah>.tar.gz. For an interactive run (although there won’t be much interaction), you can executesudo /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 or use Finder with Cmd+Shift+G to point Finder to the path. Be cautious of the file sizes, which can be around 300MB or more.
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