How Do You DiagnOSe MacOS IP Settings
Functioning of Internet Addressing
In the realm of the Internet, individuals may obtain a Public IPv4 address such as 55.232.233.120 or an IPv6 address such as 2000:7923:bbe3:7b43:52ae:d088:673f:2b3d. One can verify this information by visiting https://test-ipv6.com/. However, for those who are not technologically savvy, attempting to communicate these addresses, or even mention MAC addresses like 41:5c:a1:12:9c:c3, can become error-prone and complex. Moreover, it does not offer any historical data, especially referring to past issues.
Navigating the World Wide Web
Accessing a webpage such as https://oberbrunner-corwin.info involves initial interaction with a DNS server, which translates the host portion (oberbrunner-corwin) in combination with the Top Level Domain (info) of the URL into an IP address like 121.187.117.185. In all web requests, your computer and browser transmit their type. For instance: Mozilla/5.0 (Windows; U; Win 9x 4.90; SG; rv:1.9.2.4) Gecko/20101104 Netscape/9.1.0285
Understanding the Significance of Default Gateways
The default gateway is typically an address that is automatically configured via DHCP. You would obtain a default gateway like 192.168.155.253 (although they usually end in .1 or .254 depending on the scope size), which is where your computer directs all of its traffic to be routed onwards. There is an in-depth guide on how to address IPv6 connectivity at how-to-fix-ipv6-connectivity/ for Mac or Linux users.
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 192.168.155.253 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 fe80:6e97:bf43:d0b8:bc65%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): {143.20.131.162, 226.92.85.219}
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 41:5c:a1:12:9c:c3
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 43:9e:fd:9d:55:6c
}
Resolving Connectivity Issues for Wired and Wireless Network
When it comes to transmitting data to your router, there are two options at the physical and data layer: wired or wireless (Wi-Fi) medium.
Troubleshooting Techniques for Apple macOS / OSX
Regardless of whether you are using OSX/macOS version 10.12.9, 11.4.7, or 12.3.3, there are various tools available for resolving connectivity issues. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams that are embracing remote work and Work From Anywhere (WFA).
Utilizing Internal Scripts for Assistance
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. Additionally, the sysdiagnose tool can be used to generate a wide range of logs in a more comprehensive manner (although much of it is point-in-time related to wireless, similar to wdutil).
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. For an interactive run, you can use sudo /usr/bin/sysdiagnose and navigate to the location of the generated logs. Keep in mind that the file sizes are approximately 300MB.
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