How To Test OSX IP Settings
Understanding Internet Addressing
When using the Internet, you are allocated a unique Public IPv4 address, such as 179.146.219.73 or an IPv6 address like 2000:fd1d:f24f:aeee:409b:7958:be7a:1835. These addresses can be verified by visiting https://test-ipv6.com/. However, conveying these addresses, or even MAC addresses like b2:43:f4:d2:4f:58, to individuals unfamiliar with technology can be prone to errors and become complex quickly. In addition, it does not provide any historical data, especially when previous issues occurred.
Navigating the World Wide Web
Accessing a web page, such as https://ledner.net, entails an initial connection to a DNS server to translate the host portion (ledner) combined with the Top Level Domain (net) of the URL into an IP address, such as 50.84.13.200. Your computer and browser send their type with all web requests, for example: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko.
The Significance of Default Gateways
By default, your gateway address is automatically configured via DHCP. You receive a default gateway, such as 192.168.146.226 (typically ending in .1 or .254 depending on the scope size), to which your computer directs all its traffic for routing. For IPv6, in-depth guidance can be found in how-to-fix-ipv6-connectivity/, and such information can be checked on Mac or Linux systems with the following command:
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 192.168.146.226 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 fe80:4945:21c1:534d:280c%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): {114.162.109.58, 136.103.28.245}
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 b2:43:f4:d2:4f:58
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 67:83:0e:4f:30:dc
}
Resolving Issues with Wired and Wireless Connections
When it comes to sending data to your router, you might be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of whether your version of OSX/macOS is 10.11.7, 11.1.2, or 12.2.4, there are various tools available for troubleshooting. 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 embrace remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts
A useful tool on OSX/macOS is sudo wdutil info, which provides a dump of the current wireless related settings in the CLI and can be configured to generate specific logs for troubleshooting. Moreover, the sysdiagnose tool can be used to generate a comprehensive range of logs (although much of it is point in time only in relation to wireless, similar to wdutil).
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (although there is very little interaction), you can run sudo /usr/bin/sysdiagnose and it will display a privacy warning. When not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp or use Finder with Cmd+Shift+G to direct Finder to the path. Take note of the file sizes, which are approximately 300MB.
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