How Can I Understand Wifi Router Issues
Understanding How Internet Addresses Function
When using the Internet, it is common to have a Public IPv4 address such as 224.202.243.141 or an IPv6 address like 2000:9397:91dc:55ff:ab7:8925:12b9:7b5b. These can be verified at https://test-ipv6.com/. However, explaining these addresses, and even mentioning MAC addresses like b3:40:f8:c6:81:0c, can be prone to errors and become complex. Furthermore, this method lacks the ability to provide any historical data, particularly regarding past issues.
Navigating the World Wide Web
To access a website such as https://jacobson.name, the first step is to connect to a DNS server in order to convert the host portion (jacobson) along with the Top Level Domain (name) of the URL to an IP address, such as 157.234.0.131. It is worth noting that your computer and browser transmit their type with every web request, for example, Mozilla/5.0 (Windows; U; Win 9x 4.90; SG; rv:1.9.2.4) Gecko/20101104 Netscape/9.1.0285
The Significance of Default Gateways
The default gateway is typically an automatically assigned address through DHCP. This gateway, such as 172.28.65.50 (although it generally ends in .1 or .254 depending on the scope size), is where your computer directs all its traffic to be further routed. For IPv6, detailed instructions can be found at how-to-fix-ipv6-connectivity/, but for Mac or Linux systems, it can be checked using the following command:
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 172.28.65.50 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 fe80:7efc:cec6:de7b:e859%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): {32.138.79.11, 59.171.51.101}
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 b3:40:f8:c6:81:0c
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 db:1c:ca:b7:9b:56
}
Addressing Connectivity Issues for Wired and Wireless Networks
When it comes to transmitting data to your router, you may be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Solutions for Apple macOS / OSX Users
Regardless of whether you are running OSX or macOS, be it version 10.13.3, 11.5.1, or 12.0.2, there are various troubleshooting tools at your disposal. However, these tools do not provide a series of correlated values over time, which can be a drawback. This is where automated remote troubleshooting becomes invaluable, particularly for teams that have embraced remote work and Work From Anywhere (WFA).
Leveraging Built-in Scripts for Assistance
One useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI, and can also be configured to generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool offers a more comprehensive approach, generating a wide range of logs (albeit many are point-in-time related to wireless, similar to wdutil).
To run sudo nohup /usr/bin/sysdiagnose -u & in the background and have the logs written to /var/tmp/<blah>.tar.gz, or to run it interactively using sudo /usr/bin/sysdiagnose and navigate to the correct location in Finder, taking into account the file sizes of about 300MB.
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