How Can I Understand OSX IP Settings
The Functioning of Internet Addressing
When connecting to the Internet, you will receive a Public IPv4 address, such as 139.99.200.92, or an IPv6 address, such as 2000:2942:4e18:b046:f6d0:b59:8928:d371. You can verify this at https://test-ipv6.com/. However, communicating these addresses or MAC addresses, like fb:e3:f2:d0:78:09, can be prone to errors and can become complex quickly. Moreover, this does not provide any historical data, especially from previous issues.
Navigating the World Wide Web
To access a webpage, such as https://keebler.org, you initially contact a DNS server to convert the host name (keebler) combined with the Top Level Domain (org) of the URL into an IP address, like 237.17.169.201. When making web requests, your computer and browser actually send their type, for example Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
Understanding the Significance of Default Gateways
The default gateway is typically an automatically configured address via DHCP. You receive a default gateway, such as 172.26.87.98 (though they usually end in .1 or .254 depending on the scope size), and this is where your computer routes all its traffic. For IPv6, you can refer to how-to-fix-ipv6-connectivity/ for a detailed explanation, or check on Mac or Linux 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 172.26.87.98 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:e0b9:f44e:adc2:31db%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): {203.67.56.216, 107.207.79.42}
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 fb:e3:f2:d0:78:09
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 be:4b:75:c5:d0:87
}
Solutions for Addressing Wired and Wireless Connectivity Issues
When it comes to sending data to your router, you may encounter issues at the physical and data layer, whether you are using a wired or wireless (Wi-Fi) medium.
Troubleshooting on Apple macOS / OSX Platforms
Regardless of the version of OSX or macOS you are using, such as 10.15.2, 11.4.5, or 12.2.2, there are various troubleshooting tools available. However, relying solely on manual actions and scripts may not provide a comprehensive view of correlated values over time. This is where the role of automated remote troubleshooting becomes crucial, especially for teams that have adopted the concept of remote work and Work From Anywhere (WFA).
Leveraging Built-in Scripts for Assistance
One valuable tool on OSX/macOS is sudo wdutil info, which provides a comprehensive dump of current wireless settings to the CLI. It can also be configured to generate specific logs for troubleshooting purposes. Furthermore, the sysdiagnose tool offers a more extensive range of logs, although it primarily captures point-in-time data related to wireless settings, similar to wdutil.
To run sudo nohup /usr/bin/sysdiagnose -u & in the background and generate logs in /var/tmp/<blah>.tar.gz. If you prefer to run it interactively, you can execute sudo /usr/bin/sysdiagnose, which will prompt a privacy warning. When running it in the background, it should open Finder in the appropriate location, or you can navigate to /var/tmp using Finder with Cmd+Shift+G. Note that the file sizes are approximately 300MB.
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