How Can I Understand Mac IP Settings
Understanding Internet Addressing
When connecting to the internet, you are assigned a unique public IP address such as 17.238.117.18 for IPv4 or 2000:4fc0:1ac9:41b8:746f:9b0b:9d12:5df7 for IPv6. Checking your IP address is possible at https://test-ipv6.com/. However, conveying these addresses to non-technical individuals, or even referencing MAC addresses like 65:02:3d:1c:7e:e3 can be prone to errors and become complex. Unfortunately, this method does not provide historical data, especially when resolving past issues.
Navigating the World Wide Web
Accessing a website such as https://kuhic.io involves an initial communication with a DNS server to translate the host (kuhic) and the Top-Level Domain (io) of the URL into an IP address like 46.223.218.175. Furthermore, every web request from your computer and browser includes its type, for example: 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 address assigned automatically via DHCP, such as 192.168.18.146 (usually ending in .1 or .254, depending on the scope size). This is the point where your computer forwards all of its traffic for routing. For IPv6, detailed instructions can be found at how-to-fix-ipv6-connectivity/. On Mac or Linux, you can verify this using 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 192.168.18.146 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 fe80:9c91:eb1d:9531:4438%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): {22.28.14.212, 95.108.54.151}
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 65:02:3d:1c:7e:e3
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 22:bc:6a:a2:94:72
}
Diagnosing and Resolving Wired and Wireless Connectivity Issues
When it comes to transmitting data to your router, you might be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Steps for Troubleshooting on Apple macOS / OSX
Regardless of whether you are on OSX or macOS, whether it’s version 10.14.2, 11.1.8, or 12.1.2, there are various tools available for diagnosing connectivity issues. However, the manual actions and scripts may not provide a series of correlated values over time. This is where automated remote troubleshooting becomes valuable, especially for teams that are working remotely or following a Work From Anywhere (WFA) approach.
Useful Built-in Tools for Troubleshooting
One useful tool on OSX/macOS is the sudo wdutil info, which provides a dump of the 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, although many of them are only relevant to wireless at a specific point in time, similar to wdutil.
To run sysdiagnose in the background and save logs to /var/tmp/<blah>.tar.gz, you can use the command sudo nohup /usr/bin/sysdiagnose -u &. Alternatively, you can run it interactively with the command sudo /usr/bin/sysdiagnose, which will provide 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. However, be cautious of file sizes, which can be around 300MB or more.
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