Understand Apple IP Settings

Understanding Internet Addressing

When using the Internet, you will receive either a Public IPv4 address, such as 239.90.13.231, or an IPv6 address like 2000:3f40:105e:b22e:f816:d44a:abdf:ffa7. To verify this, visit https://test-ipv6.com/. However, attempting to convey these addresses, and even MAC addresses like 95:4b:1b:4f:9f:cc, can be error-prone and quickly become complex, especially for those unfamiliar with technical jargon. Moreover, this does not provide any historical data, particularly when previous issues occurred.

Navigation in Web Browsing

When accessing a web page like https://kunze.biz, the initial step involves contacting a DNS server to translate the host portion (kunze) combined with the Top Level Domain (biz) of the URL into an IP address, such as 44.180.197.42. With every web request, your computer and browser send its type, such as
Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36

Significance of Default Gateways

A default gateway is typically an automatically configured address via DHCP. It typically ends with .1 or .254 depending on the scope size, and serves as the point where all traffic from your computer is routed onwards. For IPv6, detailed instructions can be found at how-to-fix-ipv6-connectivity/. You can also check this on Mac or Linux with:

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  172.21.223.172    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   fe80:8567:f3e5:d9ba:7690%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): {1.206.41.229, 2.64.73.10}
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 95:4b:1b:4f:9f:cc
  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 f9:4a:d9:41:72:05
}

Troubleshooting Solutions for Wired and Wireless Networks

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

Tips for Resolving Issues on Apple macOS / OSX

Regardless of whether you are using OSX or macOS version 10.15.1, 11.2.8, or 12.3.9, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a set of correlated values over time, which is where automated remote troubleshooting becomes useful. This is especially beneficial for teams that practice remote work and Work From Anywhere (WFA).

Useful Built-in Scripts

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

To run the sysdiagnose tool in the background and generate logs in /var/tmp/<blah>.tar.gz, you can use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can use the command sudo /usr/bin/sysdiagnose, but be aware of the large file sizes of about 300MB.

Possibly Helpful Videos

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	Mac Activity Monitor - How to Troubleshoot Your Mac	Hands-On Mac
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Table 1.0 - Video Help