How Can I Support Mac Issues

The Fundamentals of Internet Addressing Systems

The Internet operates using different types of IP addresses, such as the Public IPv4 address 251.187.205.4 and the IPv6 address 2000:4e9:77f6:b966:170d:2ead:1457:e275. To verify these addresses, you can visit https://test-ipv6.com/. However, explaining and handling these addresses, including MAC addresses like 7a:dc:f8:79:41:ce, can be prone to errors and become complex. Moreover, this method does not provide historical data, especially for past issues.

Navigating the World Wide Web

When accessing a website, such as https://kub-oconnell.com, your computer first contacts a DNS server to convert the host portion (kub-oconnell) and the Top Level Domain (com) of the URL into an IP address, such as 219.238.23.121. Additionally, the computer and browser send their types with all web requests, such as
Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)

Understanding the Significance of Default Gateways

The default gateway is usually an automatically configured address through DHCP. For example, you may receive a default gateway such as 172.30.25.57 (although they typically end in .1 or .254 based on the scope size), and this is the point where your computer forwards all its traffic to be routed further. For IPv6, a detailed analysis can be found at how-to-fix-ipv6-connectivity/, but you can also 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  172.30.25.57    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   fe80:9b82:1aac:855f:63f5%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): {109.123.97.151, 89.144.158.175}
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 7a:dc:f8:79:41:ce
  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 2d:38:17:94:be:5b
}

Fixing Connectivity Issues 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.

Troubleshooting Tips for Apple’s macOS / OSX Operating Systems

Regardless of whether you are running OSX/macOS versions such as 10.11.6, 11.1.5, or 12.3.8, there is a variety of troubleshooting tools available. However, these tools do not provide a set of correlated values over time, which makes automated remote troubleshooting particularly valuable, especially for teams that embrace remote work and Work From Anywhere (WFA).

Leveraging Built-in Scripts for Assistance

One extremely useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of the current wireless settings in the command line interface (CLI). This can also be configured to generate specific logs for troubleshooting purposes. Additionally, the sysdiagnose tool offers a more comprehensive approach, generating a wide range of logs, albeit mainly point-in-time data in relation to wireless, similar to wdutil.

To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can execute sudo /usr/bin/sysdiagnose while keeping in mind the large file sizes of about 300MB or more. 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.

Possibly Helpful Videos

Video	Title	Channel
	Mac Activity Monitor - How to Troubleshoot Your Mac	Hands-On Mac
	On the Road to Big Sur 2 - Compatibility	Hands-On Mac
	Secret Mac Boot Commands - Mac Boot Key Combinations	Hands-On Mac
	macOS Big Sur - What's New in Apple macOS 11	Hands-On Mac
	Securing macOS Big Sur	Hands-On Mac

Table 1.0 - Video Help