Troubleshoot MacOS Issues
How Ip Addressing is Functioning
When using the Internet, you may receive a Public IPv4 address, for example like 27.155.210.29, or an IPv6 address such as 2000:9406:7acb:9cbd:cf6d:dce9:bbbb:f099. You can verify this at https://test-ipv6.com/. However, for individuals who are not tech-savvy, communicating these addresses, or even mentioning MAC addresses like 30:28:21:3e:c0:42, can quickly become error-prone and complicated. Moreover, this does not provide any historical data, especially when dealing with past issues.
Browsing the Web and the Process of Lookups
When accessing a website like https://kessler.co, you initially connect to a DNS server to convert the host portion (kessler) combined with the Top Level Domain (co) of the URL to an IP address, for example like 24.249.36.82. Your computer and browser sends its type with all web requests, such as Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16.
The Significance of Default Gateways
The default gateway is typically an automatically configured address through DHCP. You will receive a default gateway, for instance like 192.0.0.79 (although they usually 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, detailed instructions can be found at how-to-fix-ipv6-connectivity/, and you can check 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 192.0.0.79 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 fe80:613:1f4d:6039:a8f3%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): {203.17.221.155, 240.104.132.162}
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 30:28:21:3e:c0:42
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 d1:b0:cd:46:31:c4
}
Solutions for Wired and Wireless Connectivity Issues
When it comes to transmitting data to your router, you can use either a wired or wireless (Wi-Fi) medium at the physical and data layers.
Steps for Troubleshooting on Apple macOS / OSX
No matter which version of OSX/macOS you are currently running - whether it’s 10.14.7, 11.1.6, or 12.0.3 - there are various tools available for troubleshooting connectivity issues. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting proves to be invaluable, especially for remote work and Work From Anywhere (WFA) teams.
Utilizing Built-in Commands and Scripts
One useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can also be configured to generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool offers a more comprehensive range of logs (though much of it is only relevant at a specific point in time, similar to wdutil).
To run sysdiagnose 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, use sudo /usr/bin/sysdiagnose, but be aware of the large file sizes, around 300MB more or less.
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