How Do You DiagnOSe Wifi Router Issues
Understanding Internet Protocol Addressing
When using the Internet, one may be assigned a Public IPv4 address such as 211.123.95.224 or an IPv6 address like 2000:a402:a71c:1b4d:294e:cc8:98a4:3da5. The verification of these addresses can be done at https://test-ipv6.com/. However, the communication of these addresses, and even MAC addresses such as 34:6b:07:f2:d1:f6, can be error-prone and complex, particularly for individuals with limited technical knowledge. Furthermore, this method lacks historical data, especially in the case of past issues.
Navigating the World Wide Web
When visiting a website like https://ullrich-vonrueden.name, the first step is to access a DNS server in order to convert the host portion (ullrich-vonrueden) along with the Top Level Domain (.name) of the URL into an IP address, such as 8.162.190.161. Additionally, the computer and browser send their specifications alongside every web request e.g. Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36
Significance of Default Gateways
By default, the gateway is usually an automatically configured address through DHCP. This results in obtaining a default gateway, such as 192.168.233.7 (although they commonly end in .1 or .254 based on the scope size), which serves as the centralized point for all outgoing traffic. For those interested in IPv6, a detailed examination can be found at how-to-fix-ipv6-connectivity/, or alternatively, verification can be done on Mac or Linux by using:
route -A inet6
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 192.168.233.7 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:d1a:5b4b:2670:1485%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): {255.215.229.63, 184.40.60.148}
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 34:6b:07:f2:d1:f6
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 46:5a:ee:22:37:44
}
Troubleshooting and Resolving Connectivity Issues
In the realm of network connectivity, whether it be through a wired or wireless (Wi-Fi) medium, the transmission of data to your router takes place at the physical and data layer.
Techniques for Apple macOS / OSX Users
Irrespective of whether you are running OSX/macOS version 10.11.9, 11.5.8, or 12.2.3, there exists a variety of tools at your disposal for addressing connectivity issues. However, the manual actions and scripts available do not offer a comprehensive set of correlated values over a period of time. This is where the significance of automated remote troubleshooting comes into play, particularly for teams that are inclined towards remote work and Work From Anywhere (WFA).
Utilizing Pre-Installed Scripts for Assistance
A highly useful tool on OSX/macOS is the command sudo wdutil info, which provides a dump of the current wireless settings to the CLI and can also be configured to generate specific logs for troubleshooting purposes. Additionally, a more exhaustive approach is offered by the sysdiagnose tool, which is capable of generating a wide range of logs, although many of them are relevant only at a specific point in time, similar to the wdutil tool.
To run the sysdiagnose tool in the background and have it write logs to /var/tmp/<blah>.tar.gz, the command sudo nohup /usr/bin/sysdiagnose -u & can be used. If an interactive approach is preferred, the command sudo /usr/bin/sysdiagnose can be run, with a privacy warning being issued. When not run in the background, this command will open Finder in the correct location, otherwise, the user can navigate to /var/tmp or use Finder with Cmd+Shift+G to specify the path. It is important to be cautious of the file sizes, which typically range around 300MB.
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