DiagnOSe Apple IP Settings
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 or IPv6 address. To find out what address you have, visit https://test-ipv6.com/. Communicating these addresses, as well as MAC addresses, can be challenging and error-prone for those who aren’t technically inclined. Moreover, this method does not provide any historical data.
Navigating the World Wide Web
Accessing a web page, such as https://bayer.info, involves contacting a DNS server to convert the URL’s host (bayer) and Top Level Domain (info) into an IP address, like 72.168.12.49. Additionally, your computer and browser transmit their specifications with each web request, such as:
Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
The Significance of Default Gateways
Your default gateway is typically obtained through automatic configuration via DHCP. This gateway, such as 192.0.0.149, serves as the destination for all of your computer’s outbound traffic. For IPv6, refer to how-to-fix-ipv6-connectivity/ for detailed instructions for Mac or Linux users.
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 192.0.0.149 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 fe80:5ced:2a3d:adf3:458b%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): {71.111.207.84, 143.110.135.252}
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 f7:95:2c:86:5a:be
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 43:43:21:e3:b0:3a
}
Resolving Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you might be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX Users
No matter which version of OSX/macOS you’re using, whether it’s 10.13.8, 11.0.9, or 12.0.3, there are a variety of tools available for fixing issues. However, these manual actions and scripts don’t provide a series of correlated values over time. This is where automated remote troubleshooting becomes valuable, especially for teams that practice remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
On OSX/macOS, the sudo wdutil info command is a useful tool that provides a dump to the CLI of current wireless related settings, and it can also generate specific logs for troubleshooting. In addition, the sysdiagnose tool can be used to generate a wide range of logs, although much of it relates to a specific point in time just like 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 &. If you prefer to run it interactively, you can use sudo /usr/bin/sysdiagnose, but note that 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 using Finder with Cmd+Shift+G. Keep in mind that the file sizes are around 300MB.
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