How Do You Understand Common Wifi Connectivity
Functioning of Internet Addressing
When using the Internet, a Public IPv4 address such as 71.153.160.169 or an IPv6 address like 2000:ae57:6b1:2139:9154:30d5:1a39:c914 may be assigned. Verification can be performed at https://test-ipv6.com/. However, conveying these addresses, or referring to MAC addresses like 15:52:4d:dd:50:c0, can be prone to errors and becomes complex, particularly for non-technical users. Additionally, this method does not provide historical data, especially for past issues.
Navigating the World Wide Web
In order to access a web page such as https://rath-runolfsdottir.io, the initial step involves contacting a DNS server to convert the host portion (rath-runolfsdottir) combined with the Top Level Domain (io) of the URL into an IP address, for example: 0.67.0.67. Interestingly, with every web requests, your computer and browser convey the type, for example: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A
Significance of Default Gateways
The default gateway is typically an address automatically configured via DHCP. For instance, a default gateway like 10.182.216.246 (usually ending in .1 or .254 based on the scope size) is where your computer directs all its traffic for routing. For IPv6, detailed guidance is available at how-to-fix-ipv6-connectivity/, while verification on Mac or Linux can be done using:
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 10.182.216.246 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 fe80:2ed8:52ad:a94c:e12a%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): {133.150.53.245, 23.89.1.215}
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 15:52:4d:dd:50:c0
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 7b:67:ab:68:05:1c
}
Troubleshooting and resolving connectivity issues
When it comes to sending data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Resolving issues on Apple macOS / OSX
No matter which version of OSX/macOS you are using, whether it’s 10.11.7, 11.4.6, or 12.0.5, there are various tools available for resolving connectivity problems. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes valuable, especially for teams that embrace remote work and Work From Anywhere (WFA).
Utilizing built-in scripts
One particularly useful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting. Moreover, 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.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz for you. If you prefer an interactive approach (although there isn’t much interaction), you can run sudo /usr/bin/sysdiagnose, which will display a privacy warning. When not run in the background, it should open Finder in the correct location, allowing you to navigate to /var/tmp or use Finder with Cmd+Shift+G to point Finder to the path. Just be aware that the file sizes are approximately 300MB.
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