How Can I Understand Common Wifi Connectivity
Understanding Internet Addressing
When using the Internet, you are assigned a unique Public IPv4 address, such as 71.163.132.15, or an IPv6 address, like 2000:994e:af32:ae88:9b04:408:24bc:2c74. These addresses can be verified at https://test-ipv6.com/. However, translating and communicating these addresses, or even dealing with MAC addresses like 5e:94:17:3f:04:df, can be error-prone and complex for those who are not tech-savvy. Furthermore, historical data is not readily available, especially when troubleshooting past issues.
Navigating the World Wide Web
Accessing a website, like https://dubuque.info, involves an initial connection to a DNS server that translates the host portion (dubuque) combined with the Top Level Domain (info) of the URL into an IP address, such as 151.100.180.40. Additionally, your computer and browser include specific information with each web request, such as Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A.
The Significance of Default Gateways
The default gateway, typically assigned automatically via DHCP, is an important element in network configuration. It is represented by an address like 192.168.250.247 (although they commonly end in .1 or .254, based on the scope size), and functions as the point where your computer sends all its traffic to be routed onwards. To troubleshoot IPv6 connectivity on a Mac or Linux system, detailed instructions are available at how-to-fix-ipv6-connectivity/.
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 192.168.250.247 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 fe80:3c30:1d1d:b224:77f%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): {148.158.246.25, 62.111.251.213}
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 5e:94:17:3f:04:df
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 ac:5b:8f:fa:02:b5
}
Network Connectivity Solutions
When it comes to sending data to your router, you might be utilizing either a wired or wireless (Wi-Fi) connection at the physical and data layer.
Resolving Issues on Apple macOS / OSX
No matter which version of OSX/macOS you’re using - whether it’s 10.13.1, 11.0.9, or 12.1.6 - there are various tools available for solving connectivity problems. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes essential, especially for teams that have adopted remote work and Work From Anywhere (WFA).
Useful Built-in Utilities
A valuable tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI and can be set up to generate specific logs for troubleshooting. Moreover, the sysdiagnose tool can be used to create a wide range of logs, although many of them are only relevant to wireless issues, similar to wdutil.
To run sysdiagnose in the background and generate logs at /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 aware of the large file sizes - approximately 300MB.
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