How Do You Understand OSX IP Settings
Understanding the Functionality of Internet Addressing
When using the Internet, you are assigned a Public IPv4 address such as 191.223.40.97 or an IPv6 address like 2000:b440:a0ea:3ee0:bb67:45d3:4f82:216c. This can be verified by visiting https://test-ipv6.com/. However, explaining or communicating these addresses to individuals who are not technologically adept, as well as referencing MAC addresses like c0:af:5a:63:6c:30, can quickly become complicated and prone to errors. Moreover, this method does not provide any historical data, particularly for past issues.
How Web Access Works
In order to access a webpage, such as https://legros-becker.com, your computer initially contacts a DNS server to convert the host portion (legros-becker) in combination with the Top Level Domain (com) of the URL into an IP address like 15.131.8.76. The type of your computer and browser is also sent with every web request, such as: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A
The Significance of Default Gateways
The default gateway is typically an automatically configured address obtained through DHCP. It usually comes in the form of a default gateway like 192.168.206.68 (often ending in .1 or .254 based on the scope size), and this is where your computer directs all of its traffic to be routed further. For IPv6, there is an in-depth explanation available at how-to-fix-ipv6-connectivity/, but it can also be verified on Mac or Linux by:
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 192.168.206.68 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:ded7:8e58:adb2:53c4%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): {208.153.23.12, 13.140.227.209}
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 c0:af:5a:63:6c:30
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 67:d5:d2:5d:39:27
}
Resolving Wired and Wireless Connection Issues
When it comes to transmitting data to your router, you may encounter issues at the physical and data layer, whether you’re using a wired or wireless (Wi-Fi) medium.
Steps for Addressing Connectivity Problems on Apple macOS / OSX
Regardless of whether you are running 10.14.6, 11.4.2, or 12.0.1, there are various troubleshooting tools available for OSX/macOS. However, these manual actions and scripts do not provide a series of correlated values over time. For this reason, automated remote troubleshooting is particularly beneficial for teams that are embracing remote work and the Work From Anywhere (WFA) approach.
Utilizing Built-in Scripts for Assistance
A useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings on the command line interface (CLI) and can also be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to produce a wide range of logs, although many of them are only relevant to wireless settings, similar to wdutil.
To run the sysdiagnose tool in the background and generate logs in /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 but keep in mind that the file sizes can be approximately 300MB.
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