How Can I Understand MacOS Internet Connection
Understanding the Mechanism of Internet Addressing
When browsing the Internet, you are assigned with a Public IPv4 address such as 6.188.0.248 or an IPv6 address like 2000:b75c:5b05:d4cc:78c9:d346:5520:24b8. You can verify this information by visiting https://test-ipv6.com/. However, conveying these addresses to individuals who are not well-versed in technology or even mentioning MAC addresses like 4c:bc:b2:bd:ba:d8 can be prone to errors and become complex. Moreover, this does not provide any historical data, especially when previous issues arose.
Navigating Through the World Wide Web
In order to access a website such as https://wiza.name, the first step is to connect to a DNS server to convert the host segment (wiza) along with the Top Level Domain (name) of the URL into an IP address such as 108.64.167.139. When making web requests, your computer and browser actually transmits its type e.g. Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
Significance of Default Gateway
Typically, the default gateway is an automatically configured address through DHCP. You are assigned a default gateway such as 10.81.217.100 (although they generally end in .1 or .254 based on the scope size) and this serves as the point where your computer forwards all its traffic for routing. For IPv6, a detailed examination is available at how-to-fix-ipv6-connectivity/ but you can verify this on Mac or Linux 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 10.81.217.100 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 fe80:2ab2:dab2:3893:4acd%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): {217.220.51.21, 11.34.124.5}
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 4c:bc:b2:bd:ba:d8
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 53:00:ce:bd:d0:f5
}
Fixing Wired and Wireless Connection Issues
When it comes to transmitting data to your router, you could be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of whether you’re using OSX/macOS versions like 10.15.7, 11.1.3, or 12.1.8, there are various tools available for troubleshooting. However, these manual actions and scripts fail to provide a series of correlated values over time. This is where automated remote troubleshooting proves to be especially beneficial for teams that embrace remote work and Work From Anywhere (WFA).
Useful Built-in Tools
One particularly useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the command line interface 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 specific to a point in time in relation to wireless, similar to wdutil.
Running the command sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (although there isn’t much interaction), you can execute sudo /usr/bin/sysdiagnose and it will generate a privacy warning. When not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp using Finder with Cmd+Shift+G. It’s important to note that the file sizes are approximately 300MB, more or less.
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