Fix Mac IP Settings
Understanding the Functionality of Internet Addressing
When using the internet, you will be assigned a Public IPv4 address or an IPv6 address. One can verify this assignment by using a tool like https://test-ipv6.com/. However, conveying these addresses or MAC addresses to individuals without a technical background can be prone to error and quickly become complex. Furthermore, this method lacks historical data, especially for past issues.
Navigating the World Wide Web
Accessing a website like https://wilderman.name involves first contacting a DNS server to convert the host portion and Top Level Domain of the URL into an IP address. When making web requests, your computer and browser send specific information, such as 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
The default gateway, typically automatically assigned by DHCP, is an essential component. This gateway, usually ending in .1 or .254, depending on the scope size, is where all of your computer’s traffic is routed. For IPv6, detailed guidance can be found at how-to-fix-ipv6-connectivity/, while Mac and Linux users can employ the following command to check:
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 10.149.60.231 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 fe80:692d:8c1d:6adc:a4c0%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): {210.118.57.21, 21.73.150.249}
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 36:5a:95:2b:8c:f5
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 da:d5:ec:1c:0c:8f
}
Solutions for Resolving Wired vs. Wireless 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.
Tips for Addressing Problems on Apple macOS / OSX Systems
No matter which version of OSX/macOS you’re running, whether it’s 10.13.5, 11.2.7, or 12.2.1, there are various troubleshooting tools available. However, these manual actions and scripts don’t provide a set of correlated values over time. This is where automated remote troubleshooting becomes invaluable, particularly for teams that embrace remote work and Work From Anywhere (WFA).
Pre-Installed Utilities That Can Offer Assistance
One incredibly useful tool on OSX/macOS is the sudo wdutil info, which provides a dump to the CLI of current wireless related settings, and can also be configured to generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant to wireless at a specific point in time, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & will execute it in the background and write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (even though there isn’t much interaction), you can use sudo /usr/bin/sysdiagnose, which will prompt a privacy warning. If 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. Just be mindful of the file sizes, which are approximately 300MB or thereabouts.
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