Troubleshoot Wifi Router Issues
Understanding Internet Addressing
When using the Internet, you are assigned a specific public IP address, which can be in the form of an IPv4 address such as 103.114.95.152 or an IPv6 address like 2000:e1a0:2cc1:f0b4:d6b:43aa:dcd9:efa3. Verifying this information is possible by visiting https://test-ipv6.com/. However, explaining and working with these addresses, as well as MAC addresses like f8:78:a4:12:fe:db, can be challenging and prone to errors, especially for those who are not technologically inclined. Additionally, this method does not provide historical data, which is crucial for resolving past issues.
Navigating the World Wide Web
When attempting to access a website, such as https://hansen-lang.org, the first step is to contact a DNS server to translate the combination of the host portion (hansen-lang) and the Top Level Domain (org) of the URL into an IP address, which could be 219.160.3.91. It’s important to note that your computer and browser also transmit their type with every web request, such as Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
The Significance of Default Gateways
The default gateway, typically acquired through automatic address configuration via DHCP, is essential. It is the address, like 172.16.126.100 (commonly ending in .1 or .254 based on the scope size), where your computer directs all its traffic to be routed onward. For information on troubleshooting IPv6, a comprehensive guide can be found at how-to-fix-ipv6-connectivity/. Moreover, Mac or Linux users can verify this information as well.
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 172.16.126.100 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:a608:44d8:c2dd:8600%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): {57.66.158.45, 26.139.224.183}
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 f8:78:a4:12:fe:db
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 60:f4:9c:d3:51:28
}
Solutions for Wired and Wireless Connectivity Issues
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.
Steps to Resolve Issues on Apple macOS / OSX
Irrespective of the version of OSX/macOS you are using, whether it’s 10.13.5, 11.4.1, or 12.2.8, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting stands out, especially for teams that promote remote work and Work From Anywhere (WFA).
Useful Built-in Tools
One very useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although many are only relevant to wireless settings, similar to wdutil.
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, use the command sudo /usr/bin/sysdiagnose but be aware that it comes with a privacy warning. The file size is approximately 300MB.
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