How Can I DiagnOSe OSX Issues
Understanding Internet Addressing
When using the Internet, you will be assigned a Public IPv4 address such as 198.133.105.177 or an IPv6 address like 2000:c01:7126:523b:24e9:2e0:a8bf:dcf. These can be verified at https://test-ipv6.com/. However, conveying these addresses to non-technical users, or even referencing MAC addresses like 20:69:2a:d6:05:f4, can be prone to errors and can become complex. Furthermore, this method does not provide historical data, particularly for past issues.
Navigating the World Wide Web
In order to visit a website like https://douglas-graham.biz, the first step is to access a DNS server to convert the host portion (douglas-graham) and the Top Level Domain (biz) of the URL into an IP address, such as 210.143.247.157. Furthermore, your computer and browser transmit their information with every web request, for example: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36
The Significance of Default Gateways
Your default gateway is usually an address that is automatically configured via DHCP. This address, such as 172.31.130.210 (commonly ending in .1 or .254 depending on the scope size), is where all your computer’s traffic is sent to be routed onwards. For IPv6, a detailed explanation is available at how-to-fix-ipv6-connectivity/, and can be checked on Mac or Linux using the following method:
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 172.31.130.210 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 fe80:322e:9bfa:79f2:4e52%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): {12.151.128.15, 233.112.2.223}
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 20:69:2a:d6:05:f4
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 b3:49:97:af:74:ac
}
Resolving Connectivity Issues for Wired and Wireless Networks
When it comes to transmitting data to your router, you may choose to use either a wired or wireless (Wi-Fi) connection at the physical and data layers.
Troubleshooting Tips for Apple macOS / OSX
Regardless of whether you are running OSX/macOS version 10.11.4, 11.4.4, or 12.3.9, there are various troubleshooting tools available. However, these tools do not provide a comprehensive set of correlated values over time, which is where automated remote troubleshooting becomes invaluable, especially for teams that have embraced remote work and the Work From Anywhere (WFA) concept.
Useful Built-in Scripts
One useful tool on OSX/macOS is the sudo wdutil info, which provides a dump of the current wireless settings to the CLI and allows for the generation of specific troubleshooting logs. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of the information is only relevant to a specific moment in time, similar to wdutil.
sudo nohup /usr/bin/sysdiagnose -u & can be used to run sysdiagnose in the background and it will write logs to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively (even though there is minimal interaction), you can usesudo /usr/bin/sysdiagnose, which will prompt 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 point Finder to the path. Keep in mind that the file sizes are approximately 300MB.
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