How To Understand Apple Issues
Understanding Internet Addressing
When connecting to the Internet, you are assigned an IP address, such as the Public IPv4 address 50.132.83.223 or an IPv6 address like 2000:17d2:1b8:c389:8f29:8af7:f1cc:fc3a. These can be verified through https://test-ipv6.com/. However, communicating these addresses or MAC addresses such as a4:32:53:27:21:12 can be error-prone and complicated for those who are not tech-savvy. Furthermore, it does not provide historical data, particularly when dealing with past issues.
Navigating the World Wide Web
When attempting to access a web page, such as https://turner-rutherford.com, the process begins by reaching out to a DNS server to translate the host portion (turner-rutherford) integrated with the Top Level Domain (com) of the URL into an IP address, such as 73.155.248.80. Interestingly, your computer and browser transmit their type with all web requests, as evidenced by the example: Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
Significance of Default Gateways
The default gateway is typically an address that is automatically configured via DHCP. This address, such as 10.116.81.234 (which usually ends in .1 or .254 depending on the scope size), serves as the point where your computer dispatches all its traffic to be directed elsewhere. For IPv6, there is an in-depth guide available at how-to-fix-ipv6-connectivity/. Additionally, the default gateway on Mac or Linux can be checked utilizing the following commands:
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 10.116.81.234 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:b5d5:c48c:8255:5c66%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): {92.47.77.15, 239.169.178.160}
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 a4:32:53:27:21:12
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 47:40:a3:64:61:27
}
Resolving Issues with Wired and Wireless Connections
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.
Troubleshooting Tips for Apple macOS / OSX Users
No matter which version of OSX/macOS you are currently running, whether it’s 10.14.8, 11.0.7, or 12.1.3, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes particularly useful, especially for teams that are embracing remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One useful tool for OSX/macOS is sudo wdutil info, which provides a dump of the current wireless related settings to the CLI and can also be configured to generate specific logs for troubleshooting. In addition, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant to wireless settings at a particular point in time, just like wdutil.
To run sysdiagnose in the background and write logs to /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 sudo /usr/bin/sysdiagnose, although there is not much interaction involved. Just be mindful of the file sizes, which are approximately 300MB.
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