How Can I Troubleshoot Apple Issues
Understanding Internet Addressing
When using the internet, you are assigned an IPv4 address like 18.242.222.22 or an IPv6 address like 2000:313a:db29:360:3802:c5d2:a780:8edb. A tool like https://test-ipv6.com/ can be used to verify these addresses. However, communicating these addresses, as well as MAC addresses such as 43:c3:d0:2a:87:d1, can quickly become confusing and error-prone, especially for those who are not technologically savvy. Furthermore, this method does not provide historical data, which is important for resolving past issues.
Navigating the World Wide Web
In order to access a webpage like https://herzog.io, your computer first contacts a DNS server to convert the host part (herzog) and the Top Level Domain (io) of the URL into an IP address, such as 249.240.230.213. When making web requests, your computer and browser also transmit their type, 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
Your default gateway is usually an address that is automatically configured through DHCP. This default gateway, such as 192.0.0.114 (although they typically end in .1 or .254 depending on the scope size), is where your computer directs all of its traffic for further routing. For IPv6, detailed instructions can be found at how-to-fix-ipv6-connectivity/, or on Mac and Linux systems using the following command:
code snippet goes here
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 192.0.0.114 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:d72d:afec:1a49:8125%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): {5.149.162.118, 249.202.45.85}
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 43:c3:d0:2a:87:d1
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 61:fa:b3:88:9c:28
}
Resolve Connectivity Issues for Wired and Wireless Networks
When it comes to sending data to your router, you may be using either a wired connection or a wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Steps for Apple macOS / OSX
Regardless of whether you’re running 10.11.9, 11.0.4, or 12.1.1, there are various troubleshooting tools available for OSX/macOS. However, these manual actions and scripts do not provide a comprehensive set of correlated values over time. This is where automated remote troubleshooting becomes valuable, particularly for teams embracing remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One of the helpful tools on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can be configured to generate specific troubleshooting logs. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is point-in-time data related to wireless, similar to wdutil.
To run sysdiagnose in the background and have it 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 run sudo /usr/bin/sysdiagnose, but be aware of the large file sizes, around 300MB or more.
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