How To DiagnOSe Apple Connectivity

Understanding Network Addressing

When using the Internet, you will be assigned a Public IPv4 address such as 81.68.176.136 or an IPv6 address like 2000:3bb6:82b5:32d7:53ae:f091:6434:a10e. These can be verified at https://test-ipv6.com/. However, for individuals who are not technologically inclined, conveying or identifying these addresses, as well as MAC addresses like dd:cd:5c:e5:de:52, can be prone to errors and quickly become complicated. In addition, this method does not provide historical data, especially for past issues.

Navigating the World Wide Web

Accessing a webpage such as https://ernser.net requires initial contact with a DNS server in order to translate the host portion (ernser) combined with the Top Level Domain (net) of the URL into an IP address, such as 11.204.113.49. Moreover, your computer and browser include its type in all web requests, for example:
Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36

Understanding the Significance of Default Gateways

The default gateway is generally an automatically configured address via DHCP. Enterprises typically utilize a default gateway like 192.168.246.71 (commonly ending in .1 or .254, depending on the scope size) to route all computer traffic. For a comprehensive understanding of IPv6, refer to our detailed analysis at how-to-fix-ipv6-connectivity/ or perform a 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  192.168.246.71    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   fe80:3c21:84c:b337:26ae%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): {72.107.227.4, 248.17.168.199}
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 dd:cd:5c:e5:de:52
  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 d0:dc:a2:dc:9c:23
}

Resolving Issues with Wired or Wireless Connections

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

Troubleshooting Tips for Apple’s macOS / OSX

Regardless of the version of OSX/macOS you have - whether it’s 10.14.5, 11.0.7, or 12.2.3 - there are various tools available for resolving issues. However, these manual actions and scripts do not provide a series of correlated values over time. This is where remote troubleshooting automation becomes valuable, especially for teams that have adopted remote work and Work From Anywhere (WFA) practices.

Useful Built-in Scripts

One beneficial tool on OSX/macOS is “sudo wdutil info,” which provides a dump of the current wireless settings to the CLI, and can also be configured to generate specific troubleshooting logs. Additionally, the “sysdiagnose” tool can be used to generate a wide range of logs, although it primarily provides point-in-time information in relation to wireless, similar to wdutil.

To run it in the background and write logs to “/var/tmp/.tar.gz,” use the command “sudo nohup /usr/bin/sysdiagnose -u &”. If you prefer to run it interactively, use “sudo /usr/bin/sysdiagnose,” which will display a privacy warning. When not run in the background, it will open Finder in the correct location, or you can navigate to “/var/tmp” using Finder with Cmd+Shift+G. Just keep in mind that the file sizes are approximately 300MB.

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