Fix OSX IP Settings
Explanation of Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 233.243.180.16, or an IPv6 address, such as 2000:f11c:dbe0:df32:28e:b90c:34db:26b4. If you want to verify your address, you can visit https://test-ipv6.com/. However, explaining these addresses, or even mentioning MAC addresses like 27:fb:21:f4:bb:b7, to individuals who are not well-versed in technology can be challenging and prone to error. Additionally, this method lacks historical data, especially when it comes to previous issues.
Navigating Websites
Accessing a website, such as https://reichert.info, involves initially contacting a DNS server to convert the host portion (reichert) along with the Top Level Domain (info) of the URL into an IP address like 247.250.99.237. Your computer and browser include the type with all web requests, for example: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A.
Understanding the Significance of Default Gateways
Typically, your default gateway is an automatically configured address through DHCP, resulting in a default gateway like 10.45.162.70 (usually ending in .1 or .254 based on the scope size). This is the location where your computer forwards all its traffic for further routing. If you want to learn more about IPv6, you can explore detailed information in our article how-to-fix-ipv6-connectivity/. On Mac or Linux, you can check this information 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 10.45.162.70 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:c13d:1605:e957:846%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): {93.184.86.202, 143.233.235.86}
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 27:fb:21:f4:bb:b7
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 2c:30:8c:88:ee:c6
}
Resolving Connectivity Issues for Wired and Wireless Networks
When it comes to sending data to your router, you may be utilizing a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Solutions for Apple’s macOS / OSX
Regardless of the version of OSX/macOS you are using, such as 10.15.9, 11.6.4, or 12.1.6, there are various tools available for resolving connectivity issues. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes valuable, especially for teams that adopt remote work and the Work From Anywhere (WFA) approach.
Utilizing Built-in Scripts for Assistance
A helpful tool on OSX/macOS is the sudo wdutil info, which provides a dump of current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can generate a wide range of logs, although much of it is related to wireless settings 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. If you prefer to run it interactively, you can use sudo /usr/bin/sysdiagnose, which will prompt a privacy warning. Running it in the background should open Finder in the correct location, and for interactive runs, you can navigate to /var/tmp or use Finder with Cmd+Shift+G to locate the path. Keep in mind that the file sizes are approximately 300MB or less.
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