How To Understand MacOS IP Settings

Understanding Internet Addressing

When using the Internet, you are assigned a Public IPv4 or IPv6 address. These addresses can be checked using tools like https://test-ipv6.com/, and they play a crucial role in communication. However, conveying and managing these addresses, including MAC addresses, can be complex. Furthermore, it is important to have access to historical data, especially when previous issues occurred.

Navigating the World Wide Web

Accessing a web page, such as https://goyette-reinger.io, involves interacting with a DNS server to translate the URL into an IP address. Your computer and browser also provide information about their type with every web request. This process is vital for seamless web browsing.

The Significance of Default Gateways

The default gateway, typically assigned through DHCP, serves as a pivotal point for routing traffic on a network. Whether using an IPv4 or IPv6 gateway, understanding how to configure and manage them is essential for efficient network operation.

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  172.19.211.9    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   fe80:888c:90e5:33ba:4d80%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): {92.203.169.126, 199.98.106.71}
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 40:c1:94:9c:96:75
  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 3e:45:c8:e1:1d:fe
}

Addressing Connectivity Issues for Wired and Wireless Networks

When it comes to sending data to your router, you might be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.

Tips for Resolving Problems on Apple macOS / OSX

Regardless of which version of OSX/macOS you are running - whether it’s 10.11.9, 11.3.5, or 12.0.7 - there are various troubleshooting tools available. However, these manual actions and scripts do not provide a set of interconnected values over time. This is where automated remote troubleshooting becomes valuable, especially for teams that support remote work and Work From Anywhere (WFA).

Utilizing In-Built Scripts for Assistance

One helpful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can also generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only related to wireless at a particular point in time, similar to wdutil.

Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively, you can use 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 cautious of file sizes, which are typically around 300MB.

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Table 1.0 - Video Help