DiagnOSe Mac IP Settings
Demystifying Internet Addressing
When using the Internet, it is common to be assigned either a Public IPv4 address such as 131.131.134.62 or an IPv6 address like 2000:9653:587a:308e:7d6f:f0eb:25f6:5a22. Verification of this information can be done from https://test-ipv6.com/. However, attempting to convey these addresses to individuals who are not technologically inclined or to communicate MAC addresses like 06:da:bc:41:05:0d can become complicated. Additionally, the absence of historical data, particularly regarding past issues, poses a challenge.
Navigating the World Wide Web
When accessing a website such as https://wiza-murphy.name, the initial step involves accessing a DNS server to convert the host portion (wiza-murphy) along with the Top Level Domain (name) of the URL into an IP address, for instance, 210.53.35.18. In all web requests, your computer and browser actually transmit their type, for example: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36.
Understanding the Significance of Default Gateways
Typically configured automatically via DHCP, your default gateway is a critical address to receive. An example of a default gateway is 10.142.10.158 (usually ending in .1 or .254 depending on the scope size), and this is where your computer directs all traffic for routing. For IPv6, more detailed instructions can be found at how-to-fix-ipv6-connectivity/, while on Mac or Linux this can be checked with the following command:
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 10.142.10.158 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:d5b2:2522:e0e:d35b%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): {151.45.210.88, 246.152.87.32}
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 06:da:bc:41:05:0d
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 87:f3:bf:e7:21:c0
}
Solutions for Resolving Wired and Wireless Connectivity Issues
When it comes to transmitting data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Guide for Apple macOS / OSX
Regardless of whether you are operating on OSX/macOS such as 10.11.1, 11.4.1, or 12.2.5, there are various resources available for resolving connectivity problems. However, manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes particularly useful, especially for teams that embrace remote work and Work From Anywhere (WFA).
Useful Built-in Tools
An advantageous 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. Moreover, the sysdiagnose tool can be utilized to generate a plethora of logs, although much of it is only relevant to wireless connectivity, 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, use the command sudo /usr/bin/sysdiagnose, which will prompt a privacy warning and open Finder in the correct location for accessing the logs. Keep in mind that the file sizes are approximately 300MB.
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