How Can I Check Apple Connectivity

The Mechanism Behind Internet Addressing

When using the Internet, you are assigned a unique Public IPv4 address, such as 96.46.211.243, or an IPv6 address, such as 2000:ab77:e744:b5d4:632:aa4b:d3c3:8409. Verification of these addresses can be done at https://test-ipv6.com/. However, for those without technical expertise, attempting to communicate these addresses or even referencing MAC addresses like 3d:6b:20:e9:43:47 can be prone to error and quickly become complex. Moreover, this method lacks historical data, especially in resolving past issues.

Navigating the World Wide Web

Accessing a web page, such as https://windler.info, initially involves contacting a DNS server to convert the combination of the host portion (windler) and the Top Level Domain (info) of the URL into an IP address, such as 251.84.132.217. When making web requests, your computer and browser actually send its type, like this:
Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko.

Understanding the Significance of Default Gateways

Typically, your default gateway is an address automatically configured via DHCP, such as 192.168.104.200 (although they typically end in .1 or .254 depending on the scope size). This is the location where your computer sends all its traffic to be routed onwards. For IPv6, a detailed guide on how-to-fix-ipv6-connectivity/ is available, or you can use Mac or Linux to check 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  192.168.104.200    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:ada2:f5eb:26fe:904b%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): {4.252.180.106, 28.152.9.120}
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 3d:6b:20:e9:43:47
  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 22:5b:12:3e:53:e9
}

Resolve Issues with Wired or Wireless Connections

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

Troubleshooting on Apple macOS / OSX

Irrespective of whether you are running OSX/macOS version 10.15.4, 11.1.4, or 12.3.7, there are numerous troubleshooting tools available. However, these manual interventions and scripts do not provide a set of interconnected values over time. This is where automated remote troubleshooting becomes invaluable, particularly for teams adopting remote work and the Work From Anywhere (WFA) approach.

Useful Built-in Scripts

A highly useful tool on OSX/macOS is the sudo wdutil info, which dumps the current wireless settings to the CLI and can also be set up to generate specific troubleshooting logs. In addition, the more comprehensive sysdiagnose tool can be used to generate a wide range of logs (although many are only relevant to wireless at a specific point in time, similar to wdutil).

Running sudo nohup /usr/bin/sysdiagnose -u & will execute it in the background and write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (even though there is minimal interaction), you can use the command
sudo /usr/bin/sysdiagnose, which will display 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 direct Finder to the path. However, be mindful of the file sizes, which are around 300MB more or less.

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