How To Understand Mac Internet Connection
Basics of Internet Addressing
When using the Internet, you are assigned a unique Public IPv4 address, such as 41.226.104.206, or an IPv6 address, like 2000:a9ef:26e3:b03e:dfc8:db18:36a0:4bc1. Verifying this information can be done through https://test-ipv6.com/. However, for those who are not well-versed in technology, relaying or even identifying these addresses, as well as MAC addresses like 5f:24:45:cd:ea:cd, can be prone to errors and quickly become complex. Furthermore, this process does not provide any historical data, especially regarding past issues.
Navigating the World Wide Web
When attempting to reach a webpage, such as https://donnelly.com, the first step is to access a DNS server to translate the host portion (donnelly) in conjunction with the Top Level Domain (com) of the URL to an IP address, such as 76.110.255.10. Every web request sent from your computer and browser actually contains its type, such as Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16.
Understanding the Significance of Default Gateways
In most cases, your default gateway is automatically configured through DHCP and is assigned an address, like 172.21.71.59 (typically ending in .1 or .254 depending on the scope size). This is the location where your computer routes all of its traffic. A deeper exploration of IPv6 connectivity is available at how-to-fix-ipv6-connectivity/, or alternatively, you can verify this on Mac or Linux with 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 172.21.71.59 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:ea0a:bf58:893:1bdf%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): {226.12.135.111, 65.52.8.98}
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 5f:24:45:cd:ea:cd
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 b9:b6:c6:5b:95:fe
}
Addressing Wired and Wireless Connectivity Issues
When it comes to sending data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Solutions for Apple macOS / OSX Users
Regardless of whether you are working with OSX/macOS versions such as 10.12.9, 11.4.1, or 12.3.6, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a set of correlated values over time, which is where automated remote troubleshooting becomes valuable, especially for remote work and Work From Anywhere (WFA) teams.
Effective Built-in Scripts for Troubleshooting
A useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can also be configured to generate specific troubleshooting logs. Additionally, the sysdiagnose tool offers a comprehensive range of logs, although much of it is only point-in-time in relation to wireless, similar to wdutil.
To run the sysdiagnose tool in the background and generate logs, the command sudo nohup /usr/bin/sysdiagnose -u & can be used. Alternatively, for interactive use, the command sudo /usr/bin/sysdiagnose will provide a privacy warning and open Finder in the correct location, or users can navigate to /var/tmp using Finder with Cmd+Shift+G. It’s important to note that the file sizes are approximately 300MB.
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