How Do You Understand Mac IP Settings

Explaining Internet Addressing

When using the Internet, individuals may receive a Public IPv4 address such as 93.214.11.207 or an IPv6 address like 2000:5208:3496:c6ff:eae0:1402:5ae4:464d. The verification for these addresses can be done at https://test-ipv6.com/. However, explaining or relaying these addresses, as well as MAC addresses like 4d:d9:cb:de:80:b5, to individuals who may not be tech-savvy can be prone to errors and can quickly become complex. Furthermore, this method does not provide any historical data, especially regarding previous issues.

Navigating the World Wide Web

When accessing a website such as https://hills.net, the first step involves connecting to a DNS server to convert the host portion (hills) combined with the Top Level Domain (net) of the URL into an IP address such as 227.229.162.63. Additionally, each web request sent from your computer and browser includes information regarding its 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

Typically, the default gateway is an automatically configured address provided through DHCP. This default gateway, such as 192.0.0.140 (although they usually end in .1 or .254 depending on the scope size), is where all the outgoing traffic from your computer is routed. For a more detailed explanation regarding IPv6 connectivity, a guide can be found at how-to-fix-ipv6-connectivity/, or alternatively, it can be checked 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  192.0.0.140    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   fe80:447:d2f6:71e6:22ce%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): {234.88.198.204, 242.232.130.245}
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 4d:d9:cb:de:80:b5
  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 86:9c:7f:29:4a:d0
}

Solutions for Wired and Wireless Connectivity Issues

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

How to Address Problems on Apple macOS / OSX

Irrespective of whether you are running OSX/macOS version 10.12.6, 11.5.5, or 12.2.7, there are various troubleshooting tools available. However, these manual actions and scripts often fail to provide a consistent set of correlated values over time. This is where automated remote troubleshooting proves to be extremely beneficial, especially for teams that have adopted remote work and Work From Anywhere (WFA) practices.

Useful Built-in Scripts

One of the most valuable tools on OSX/macOS is the sudo wdutil info command, which provides a dump of the current wireless settings to the CLI and can be configured to generate specific troubleshooting logs. Additionally, the sysdiagnose tool offers a more comprehensive range of logs (although much of it is only relevant to wireless at a specific point in time, similar to wdutil).

Running sudo nohup /usr/bin/sysdiagnose -u & will execute the tool in the background and generate logs in /var/tmp/<blah>.tar.gz. If you prefer to run it interactively (although there is minimal interaction), you can use the command
sudo /usr/bin/sysdiagnose, which will trigger a privacy warning. When not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp or use Finder with Cmd+Shift+G to locate the path. Keep in mind that the file sizes are approximately 300MB, give or take.

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