How To Test MacOS IP Settings
The Functioning of Internet Addressing
When using the Internet, you will be assigned a Public IPv4 address, such as 17.214.83.39, or an IPv6 address, such as 2000:a15c:e9dd:9ab8:70e3:e531:17e4:6877. To verify this information, you can use https://test-ipv6.com/. However, for individuals who are not familiar with technical aspects, communicating these addresses, or even referencing MAC addresses like 9e:8b:92:8a:25:08, can prove to be difficult and prone to errors. Moreover, this method does not provide any historical data, particularly with regards to past issues.
Navigating the Internet
In order to access a website such as https://becker.biz, you first need to connect to a DNS server to translate the host section (becker) in combination with the Top Level Domain (biz) of the URL to an IP address, such as 189.93.27.31. Additionally, every web request from your computer and browser contains information about its type, such as Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)
The Significance of Default Gateways
The default gateway is typically an automatically configured address through DHCP. It usually appears as a default gateway like 192.0.0.224, although they usually end in .1 or .254 based on the scope size. This is where your computer sends all its traffic to be further routed. For IPv6, there is an extensive guide available at how-to-fix-ipv6-connectivity/, and you can verify this on Mac or Linux using the following commands:
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 192.0.0.224 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 fe80:57d7:f779:5d2c:e5ce%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): {176.253.191.192, 19.161.37.94}
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 9e:8b:92:8a:25:08
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 1e:9d:f4:00:7e:2b
}
Solutions for Wired and Wireless Connectivity Issues
When it comes to transmitting data to your router, you may encounter issues at the physical and data layers, whether you are using a wired or wireless (Wi-Fi) connection.
Tips for Troubleshooting on Apple macOS / OSX
Regardless of the version of OSX/macOS you are using, whether it’s 10.14.4, 11.4.4, or 12.0.3, there are various tools available for troubleshooting. However, these tools may not provide a set of interconnected values over time. This is where automated remote troubleshooting becomes essential, particularly for teams that have embraced remote work and the Work From Anywhere (WFA) culture.
Useful Built-in Scripts
One useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of the current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although many of them are only relevant at a specific point in time, similar to wdutil.
To run the sysdiagnose tool in the background and write logs to /var/tmp/<blah>.tar.gz, you can use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can use the command sudo /usr/bin/sysdiagnose, although it will display 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. Keep in mind that the file sizes are around 300MB.
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