How To Troubleshoot OSX Issues
The Functionality of Internet Addressing
When using the Internet, it is common to have either a Public IPv4 address similar to 121.196.140.204 or an IPv6 address like 2000:ed74:4799:1464:c3f:6cb2:1759:573a. You can verify this information at https://test-ipv6.com/. However, for those who are not knowledgeable in technology, communicating these addresses or MAC addresses like 47:44:26:ee:60:c5 can be prone to errors and quickly become complicated. Furthermore, this method does not provide any historical data, especially when there were previous problems.
Navigating the World Wide Web
When trying to access a website such as https://bogan.net, the first step is to access a DNS server in order to translate the host portion (bogan) combined with the Top Level Domain (net) of the URL into an IP address like 240.18.190.39. Your computer and browser send its type with all web requests, for example Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A.
The Significance of Default Gateways
The default gateway is usually an automatically configured address via DHCP. You will receive a default gateway like 192.168.194.24 (although they typically end in .1 or .254 depending on the scope size), and this is where your computer sends all its traffic to be routed onwards. For IPv6, we offer in-depth information on how-to-fix-ipv6-connectivity/, but you can also check on Mac or Linux with:
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 192.168.194.24 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 fe80:429e:c066:dfe:c63%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): {127.65.63.98, 211.233.170.114}
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 47:44:26:ee:60:c5
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 17:e1:c1:cd:04:37
}
Solve Issues with Wired and Wireless Connections
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 the version of OSX/macOS you have, whether it’s 10.12.1, 11.2.9, or 12.2.4, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes crucial, especially for teams that embrace remote work and Work From Anywhere (WFA).
Useful Built-in Scripts for Assistance
A very useful tool on OSX/macOS is the sudo wdutil info, which provides a dump of current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting. Moreover, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant to wireless settings like wdutil.
To run the sysdiagnose tool in the background and generate logs in /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can execute the command sudo /usr/bin/sysdiagnose which 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. Just keep in mind that the file sizes are approximately 300MB.
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