Understand OSX IP Settings
Understanding the Functioning of Internet Addressing
When using the Internet, you might have a Public IPv4 address similar to 216.190.32.42 or an IPv6 address like 2000:8ad8:eaf5:cb50:6c05:7b53:2c2e:880b. Verifying this information can be done through https://test-ipv6.com/. However, for those who are not tech-savvy, relaying or referencing these addresses, or MAC addresses like 91:54:c6:fe:a1:82, can often lead to errors and become complex quickly. Moreover, this does not provide any historical data, especially from when previous issues occurred.
Navigating the World Wide Web
In order to access a website such as https://reichel.org, you initially reach out to a DNS server to convert the host portion (reichel) combined with the Top Level Domain (org) of the URL into an IP address like 45.108.167.205. Your computer and browser include its type in all web requests, for example: Mozilla/5.0 (Windows; U; Win 9x 4.90; SG; rv:1.9.2.4) Gecko/20101104 Netscape/9.1.0285
The Significance of Default Gateways
Your default gateway is generally an address that is automatically configured via DHCP. It provides you with a default gateway like 192.168.253.82 (although they generally end in .1 or .254 depending on the scope size) and this is where your computer sends all its traffic to be routed onwards. For IPv6, you can delve deeper into this by visiting how-to-fix-ipv6-connectivity/ - but on Mac or Linux, you can check using:
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 192.168.253.82 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 fe80:4ef9:1f75:108d:de78%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): {121.235.172.173, 36.216.45.105}
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 91:54:c6:fe:a1:82
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 df:c0:b8:c2:9c:65
}
Resolve Issues with Wired or 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.
Steps for Apple macOS / OSX Troubleshooting
Regardless of the version of OSX/macOS you are using, whether it’s 10.15.4, 11.1.3, or 12.1.3, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes valuable, particularly for teams that are embracing remote work and Work From Anywhere (WFA).
Utilize Built-in Scripts for Assistance
An extremely useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can also be configured to generate specific logs for troubleshooting purposes. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant at a specific point in time in relation to wireless, similar to wdutil.
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can use sudo /usr/bin/sysdiagnose, which will open Finder to the correct location or you can navigate to /var/tmp using Finder with Cmd+Shift+G. Keep in mind that the file sizes are approximately 300MB.
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