How Can I Fix OSX IP Settings
The Functionality of Internet Addressing
When connecting to the Internet, you are assigned a Public IPv4 address such as 25.19.15.70 or an IPv6 address like 2000:792a:5710:9a6c:56e1:94a9:a735:c5ff. These addresses can be verified at https://test-ipv6.com/, but conveying them to non-technical individuals or referencing MAC addresses like eb:a1:14:9d:de:49 can lead to mistakes and complexity. There is also a lack of historical data, especially concerning prior issues.
Navigating the Internet
When accessing a website like https://collins.name, the first step is to connect to a DNS server to translate the host portion (collins) along with the Top Level Domain (name) of the URL to an IP address such as 140.56.204.241. Additionally, your computer and browser send specific type information with each web request such as Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
The Significance of Default Gateways
The default gateway is typically an automatically assigned address via DHCP, such as 192.0.0.181 (often ending in .1 or .254 depending on the scope size). This is where your computer directs all traffic to be routed onwards. For IPv6, a comprehensive guide on how-to-fix-ipv6-connectivity/ is available, and on Mac or Linux, this can be verified with:
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 192.0.0.181 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:f04e:c77f:84a1:daf4%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): {15.185.107.131, 80.65.19.201}
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 eb:a1:14:9d:de:49
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 25:e6:86:43:b7:52
}
Resolving Issues with Wired or Wireless Connection
When it comes to sending data to your router, you might use a wired or wireless (Wi-Fi) medium at the physical and data layer.
Tips for Apple macOS / OSX Troubleshooting
Regardless of whether you are using OSX/macOS versions like 10.12.6, 11.4.4, or 12.3.4, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time, which is where automated remote troubleshooting becomes essential, especially for teams that adopt remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
A helpful tool on OSX/macOS is sudo wdutil info, which provides a dump to the CLI of current wireless related settings and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a variety of logs, although most are point-in-time only in relation to wireless, similar to wdutil.
To run it in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. For an interactive experience, you can run sudo /usr/bin/sysdiagnose, which will open Finder in the correct location or allow you to navigate to /var/tmp using Cmd+Shift+G in Finder. Keep in mind that the file sizes are around 300MB more or less.
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