How Can I DiagnOSe Wifi Router Issues
The Process of Internet Addressing
When connecting to the Internet, individuals are assigned a public IP address, such as 155.3.217.131 for IPv4 or 2000:78ef:3850:8819:c5fe:1b19:7fe0:d1aa for IPv6. To verify these addresses, you can visit https://test-ipv6.com/. However, conveying and utilizing these addresses, including MAC addresses like 85:63:49:b7:b0:15, can be prone to errors and become complex for non-technical users. Moreover, this method does not provide any historical data, particularly when dealing with past issues.
Navigating the Internet
In order to access a website such as https://feil.biz, you first connect to a DNS server to translate the host section (feil) and the Top Level Domain (biz) of the URL into an IP address, such as 103.200.82.185. Additionally, your computer and browser send their type with all web requests, for example: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
The Significance of Default Gateways
Your default gateway is typically an automatically assigned address through DHCP, such as 192.0.0.2 (typically ending in .1 or .254 based on the scope size). This location is where your computer directs all its traffic in order to be routed further. For IPv6, you can refer to how-to-fix-ipv6-connectivity/ for an in-depth explanation. On Mac or Linux, you can verify this by using:
ifconfig | grep "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 192.0.0.2 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 ab:3d21:dbdb:43e1:9daf:abbf:b585:6af3%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): {33.104.233.133, 206.155.196.194}
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 85:63:49:b7:b0:15
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 3d:0f:62:9e:76:40
}
Fixing Issues with Wired and Wireless Connections
When it comes to transferring data to your router, you might be utilizing either a wired or a wireless (Wi-Fi) connection at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
No matter which version of OSX/macOS you have, whether it’s 10.14.6, 11.2.6, or 12.2.5, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams that are embracing remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One extremely useful tool on OSX/macOS is sudo wdutil info, which provides a current wireless settings dump to the CLI and can also be configured to generate specific logs for troubleshooting. In addition, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant to wireless at a specific point in time, similar to wdutil.
By running sudo nohup /usr/bin/sysdiagnose -u &, you can execute it in the background and it will write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (even though there isn’t much interaction), you can runsudo /usr/bin/sysdiagnose and it will display a privacy warning. If 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 navigate to the path. Just keep in mind that the file sizes are approximately 300MB or so.
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