Understand OSX Internet
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 or IPv6 address. A Public IPv4 address would look something like 219.129.112.226, while an IPv6 address would look like 2000:8576:725f:bf77:78eb:329a:4b3b:9053. You can verify your address at https://test-ipv6.com/. However, explaining or attempting to remember these addresses, as well as MAC addresses such as 1c:c4:42:47:35:13, can be complex and prone to errors. Moreover, this method does not provide any historical data, especially when past issues need to be addressed.
Navigating the World Wide Web
Accessing a website, such as https://abshire.name, involves first connecting to a DNS server to translate the host portion (abshire) along with the Top Level Domain (name) of the URL into an IP address, for example 82.36.42.57. Additionally, your computer and browser send their information with each web request, for instance:
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A
Understanding the Significance of Default Gateways
The default gateway is typically an automatically configured address through DHCP. This results in obtaining a default gateway like 10.243.0.123 (often ending in .1 or .254 based on scope). This is where your computer sends all traffic to be routed onwards. To delve deeper into IPv6, you can visit how-to-fix-ipv6-connectivity/ or check on MacOS or Linux with the following command:
sudo route
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 10.243.0.123 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 fe80:8c47:fc7e:82d0:335%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): {104.33.212.246, 117.11.168.218}
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 1c:c4:42:47:35:13
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 61:5d:93:9a:96:b3
}
Problem Solving for Wired and Wireless Connections
When it comes to transmitting data at the physical and data layer, you may be using either a wired or wireless (Wi-Fi) medium to send the data to your router.
Tips and Tricks for Apple macOS / OSX Users
Regardless of which version of OSX/macOS you are using, whether it’s 10.15.2, 11.5.7, or 12.2.2, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes crucial, particularly for teams that are fully embracing remote work and the Work From Anywhere (WFA) concept.
Utilizing In-Built Scripts for Assistance
One incredibly useful tool on OSX/macOS is the sudo wdutil info, which provides a dump to the CLI of current wireless settings, and can be configured to generate specific logs for troubleshooting purposes. Additionally, the sysdiagnose tool is perhaps even more comprehensive, generating a wide range of logs (although much of it is point-in-time only in relation to wireless, 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 to run it interactively, you can execute sudo /usr/bin/sysdiagnose, which will prompt 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. However, be aware that the file sizes are approximately 300MB.
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