How Do You DiagnOSe Apple Issues
The Functioning of Internet Addressing
When using the Internet, one may receive a Public IPv4 address such as 105.209.164.247 or an IPv6 address like 2000:ba21:5b8e:2001:d89c:a25b:29a:2102. It is possible to verify this at https://test-ipv6.com/. However, conveying these addresses or MAC addresses like 3b:d0:0a:93:b8:28 to those who are not tech-savvy can lead to errors and complexities. Furthermore, this method does not provide historical data, especially regarding past issues.
Navigating the Internet
Accessing a web page like https://cummings-quigley.com begins with reaching out to a DNS server to convert the host portion (cummings-quigley) and the Top Level Domain (com) of the URL into an IP address, like 242.48.62.168. In fact, the computer and browser specify their type with each web request, for example: Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)
The Significance of Default Gateways
The default gateway is typically an address that is automatically configured via DHCP. You will obtain a default gateway such as 192.168.75.217 (although they usually end in .1 or .254 based on the scope size), and this is where the computer directs all its traffic for onward routing. For IPv6, there is an in-depth exploration available at how-to-fix-ipv6-connectivity/, but it can be checked 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 192.168.75.217 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 fe80:2b96:90eb:ed2f:4118%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): {86.45.45.81, 137.81.253.96}
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 3b:d0:0a:93:b8:28
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 7a:d6:a0:11:c1:4a
}
Resolving Connectivity Issues for Wired and Wireless Networks
When it comes to transmitting data to your router, you might be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of whether you’re using OSX/macOS versions such as 10.15.6, 11.1.5, or 12.2.1, there are numerous tools available for troubleshooting. However, these manual actions and scripts do not provide a series of correlated values over time, which is where automated remote troubleshooting becomes invaluable, especially for teams that embrace remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One useful tool for OSX/macOS is the 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. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is point in time only in relation to wireless, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively, you can run sudo /usr/bin/sysdiagnose and it will give a privacy warning. 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 to point Finder to the path. Be aware that the file sizes are around 300MB more or less.
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