How To DiagnOSe MacOS Issues
Understanding Internet Addressing
When using the internet, you are assigned a unique Public IPv4 or IPv6 address. The Public IPv4 address looks something like 178.240.125.68, while an IPv6 address might look like 2000:560b:f739:8a7f:e7fb:606f:13f6:faf9. Checking your assigned address can be done through a website such as https://test-ipv6.com/. However, conveying these addresses to non-technical individuals or even discussing MAC addresses like f6:04:8f:74:0a:29 can quickly become complicated and prone to errors, while lacking historical data.
Navigating the World Wide Web
Accessing a webpage such as https://brakus.net requires an initial translation of the domain name (brakus) and the Top Level Domain (net) to an IP address, for example like 103.120.47.138. Furthermore, your computer and browser transmit their specifications with every web request, as seen with the example Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko.
The Significance of Default Gateways
The default gateway is typically assigned automatically through DHCP and usually appears as an address ending in .1 or .254, depending on the scope size, such as 192.168.224.33. This is where your computer sends all its traffic to be routed onwards. For troubleshooting IPv6 connectivity on Mac or Linux, we have a detailed guide available at how-to-fix-ipv6-connectivity/.
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 192.168.224.33 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 fe80:2a1b:17c8:bda3:40b1%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): {89.179.118.84, 242.168.119.126}
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 f6:04:8f:74:0a:29
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 a1:7f:11:60:ea:e6
}
Fixing Connectivity Issues on Wired or Wireless Networks
When it comes to transferring data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
No matter the version of OSX/macOS you are using - whether it’s 10.13.8, 11.6.8, or 12.0.5, 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 crucial, especially for teams that are embracing remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One tool that is particularly helpful on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although many are only relevant to wireless settings at a specific point in time, similar to wdutil.
To run it 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 the command sudo /usr/bin/sysdiagnose, but be cautious of the large file sizes of about 300MB.
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