How Can I DiagnOSe Common Wifi Router Issues
A Guide to Internet Addressing
When using the Internet, you are given an IP address such as 35.67.185.58 or 2000:7d1d:79ca:a524:e9cf:ca4f:84e7:b742. You can verify this information at https://test-ipv6.com/. However, conveying these addresses to individuals who are not well-versed in technology, or even referencing MAC addresses like b6:f2:e4:44:61:0b, can be prone to errors and quickly becomes complex. Furthermore, this does not provide any historical data (especially from previous issues).
Navigating the Internet
In order to access a website such as https://wehner.info, you first connect to a DNS server to convert the host portion (wehner) along with the Top Level Domain (info) of the URL into an IP address like 58.5.7.48. Your computer and browser transmit its type along with all web requests e.g. Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
Understanding the Significance of Default Gateways
Typically, your default gateway is an address that is automatically configured via DHCP. You receive a default gateway such as 192.168.98.127 (although they usually end in .1 or .254 depending on the scope size), and this is where your computer forwards all of its traffic. For IPv6, you can find in-depth information at how-to-fix-ipv6-connectivity/ or you can check on Mac or Linux with:
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 192.168.98.127 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 fe80:95da:1d66:6ac9:6092%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): {6.189.153.18, 144.107.241.19}
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 b6:f2:e4:44:61:0b
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 b6:b6:83:99:23:30
}
Diagnosing and Resolving Connectivity Issues
When it comes to transmitting data to your router, you may encounter issues at the physical and data layer, especially if you are using a wired or wireless (Wi-Fi) medium.
Troubleshooting Tools for Apple macOS / OSX
Regardless of whether you are using OSX/macOS 10.14.9, 11.6.9, or 12.2.1, there are various troubleshooting tools available. However, these manual actions and scripts may not provide a consistent set of values over time. For remote teams or those working from anywhere, automated remote troubleshooting can be particularly useful.
Useful Built-in Utilities
One of the most helpful tools on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings in the Command Line Interface (CLI) and can also generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant to wireless settings at a specific point in time, similar to wdutil.
To run sudo nohup /usr/bin/sysdiagnose -u & in the background and generate logs in /var/tmp/<blah>.tar.gz, or run sudo /usr/bin/sysdiagnose interactively, which will give a privacy warning and open Finder in the correct location. The file sizes can be quite large, around 300MB. Be prepared for this when running the command.
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