How To Support MacOS IP Settings
Understanding Internet Protocol Addresses
When using the Internet, you are assigned an IP address, such as 221.235.161.206 for IPv4 or 2000:6983:97c2:23b6:a922:9d1:87e5:c9d3 for IPv6. To check your IP address, you can visit https://test-ipv6.com/. However, conveying and comprehending these addresses, as well as MAC addresses like 11:6f:21:1c:39:0f, can be challenging for non-technical individuals. Furthermore, these addresses do not provide any historical data, especially during previous issues.
Navigating the World Wide Web
When accessing a website, such as https://reilly-beatty.net, the process begins by contacting a DNS server to convert the host portion (reilly-beatty) along with the Top Level Domain (net) of the URL into an IP address like 251.189.23.122. Your computer and browser send their type along with all web requests, for example: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36
Significance of Default Gateways
The default gateway is typically an automatically configured address via DHCP. This default gateway, such as 192.168.58.54 (typically ending in .1 or .254 depending on the scope size) is where your computer directs all its traffic to be routed onwards. For IPv6, you can find detailed instructions on how-to-fix-ipv6-connectivity/, but you can also verify it on Mac or Linux by 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 192.168.58.54 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 fe80:8da5:a2bc:52b0:637%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): {84.79.235.155, 112.117.249.156}
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 11:6f:21:1c:39:0f
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 7b:28:cc:01:b3:1e
}
Resolve Connection Issues in Wired or Wireless Networks
When it comes to sending data to your router, you have the option to use a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Steps for Apple macOS / OSX
Regardless of the version of OSX/macOS you are using, whether it’s 10.15.8, 11.3.3, or 12.3.6, 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).
Useful Built-in Scripts
On OSX/macOS, the sudo wdutil info tool is very helpful as it provides a dump of the current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting. Another tool, the sysdiagnose tool, can be used to generate a wide range of logs, although it is limited to point-in-time data related to wireless, similar to wdutil.
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, you can use the command sudo nohup /usr/bin/sysdiagnose -u &. Alternatively, you can run it interactively by using the command sudo /usr/bin/sysdiagnose, which will give a privacy warning. When not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp using Finder with Cmd+Shift+G. Keep in mind that the file sizes are around 300MB more or less.
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