How To Test Apple IP Settings
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 or IPv6 address, such as 248.172.197.42 or 2000:d8e3:a3ed:a8f:d59f:614c:27aa:140b. Verification of this address can be done through https://test-ipv6.com/. However, translating and sharing these addresses, as well as MAC addresses like e8:bb:ee:8e:a8:a3, can be prone to errors and complexities, especially for those who are not well-versed in technology. Furthermore, this method does not provide any historical data, particularly for past issues.
Navigating the World Wide Web
When attempting to access a website like https://schinner.net, the first step is to connect to a DNS server in order to convert the host portion (schinner) combined with the Top Level Domain (net) of the URL into an IP address, such as 9.167.144.168. Notably, your type of computer and browser are included in all web requests, for example: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
Understanding the Significance of Default Gateways
Typically, a default gateway is automatically assigned through DHCP and appears as an address like 192.0.0.51, with a typical ending being .1 or .254 depending on the scope size. This is the location where your computer forwards all of its traffic to be routed elsewhere. For IPv6, detailed information on troubleshooting can be found at how-to-fix-ipv6-connectivity/. Furthermore, you can verify this status on Mac or Linux platforms with a deep dive.
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 192.0.0.51 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 fe80:870f:c43c:d5e7:d6d1%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): {187.69.52.186, 69.243.36.136}
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 e8:bb:ee:8e:a8:a3
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 ec:0c:ac:f9:5f:d8
}
How to Troubleshoot and Fix Connectivity Issues
When it comes to sending data to your router, you have the option of using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Resolving Connectivity Problems on Apple macOS / OSX
Regardless of whether you are using OSX/macOS version 10.15.8, 11.6.8, or 12.1.2, there are a variety of troubleshooting tools available. However, these tools do not provide a set of correlated values over time, unlike automated remote troubleshooting, which is particularly beneficial for remote work and Work From Anywhere (WFA) teams.
Useful Built-in Scripts for Troubleshooting
A helpful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can be configured to generate specific troubleshooting logs. Additionally, the sysdiagnose tool can be used to generate numerous logs related to wireless, although most of the information is point-in-time only, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz. Alternatively, running sudo /usr/bin/sysdiagnose interactively will give a privacy warning and prompt you to navigate to the correct location in Finder or use Cmd+Shift+G to point Finder to the path. Be aware that the file sizes are approximately 300MB.
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