DiagnOSe Common Wifi Issues
Understanding Internet Addressing
When using the Internet, individuals may be assigned a Public IPv4 address such as 220.255.24.3 or an IPv6 address like 2000:5ee6:a838:2146:52c0:bd62:ca8e:3275. Verification of these addresses can be done through https://test-ipv6.com/. However, conveying these addresses to those who are not technologically savvy, or even referencing MAC addresses like 3d:f0:45:0b:9c:ef, can lead to inaccuracies and complicated conversations. Additionally, this method does not provide historical data, particularly regarding previous problems that occurred.
Navigating the World Wide Web
When attempting to access a web page like https://murray.org, the initial step involves using a DNS server to convert the host portion (murray) and the Top Level Domain (org) of the URL into an IP address, such as 79.87.94.200. Interestingly, each web request sent by your computer and browser specifies its type, for example: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36
Understanding Default Gateways' Significance
Default gateways are often automatically set through DHCP and are typically assigned a default gateway like 192.0.0.191 (ending in .1 or .254 based on the scope size). This is where all of your computer’s traffic is routed. More detailed information on IPv6 can be found in the article: how-to-fix-ipv6-connectivity/. Additionally, you can check for this information on Mac or Linux by 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 192.0.0.191 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 fe80:24af:e3bf:9c1a:4d69%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): {161.26.16.219, 139.20.25.224}
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 3d:f0:45:0b:9c:ef
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 b8:51:d3:6e:06:1e
}
Fixing Connectivity Issues for Wired and Wireless Networks
When it comes to transmitting data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Tips for Troubleshooting on Apple macOS / OSX
No matter which version of OSX/macOS you are using, whether it’s 10.12.1, 11.6.6, or 12.1.2, 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 proves to be beneficial, especially for teams that are shifting towards remote work and embracing the concept of Work From Anywhere (WFA).
Useful Built-in Scripts
One extremely helpful tool on OSX/macOS is the sudo wdutil info, which provides a dump of current wireless related settings to the CLI, and can also be configured to generate specific logs for troubleshooting purposes. Moreover, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only point-in-time information in relation to wireless, similar to wdutil.
To run it in the background and have it write logs to /var/tmp/<blah>.tar.gz, you can use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can use sudo /usr/bin/sysdiagnose, but be mindful of the large file sizes, which are typically around 300MB.
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