How Do You DiagnOSe OSX IP Settings
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 or IPv6 address. These addresses can be checked through websites like https://test-ipv6.com/. However, for those who are not familiar with technical details, communicating or referencing these addresses, as well as MAC addresses, can be challenging. Moreover, it does not provide historical data of previous issues.
Navigating the World Wide Web
Accessing a website such as https://schimmel.info involves contacting a DNS server to translate the URL host and Top Level Domain into an IP address, like 209.156.16.199. Your computer and browser also send their specifications with every web request, for example: Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
The Significance of Default Gateways
The default gateway, typically obtained through DHCP, serves as the address to which your computer directs all outgoing traffic. This address, such as 172.16.210.48, usually ends in .1 or .254 depending on the scope size. For IPv6, detailed instructions can be found here, and can be checked on Mac or Linux using:
command here
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 172.16.210.48 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:ec33:c8d1:cf94:bf90%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): {241.169.130.67, 205.188.90.127}
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 3e:3f:00:2e:0b:9d
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 1e:5c:c6:a4:84:a4
}
Resolving Connectivity Issues for Wired and Wireless Networks
When it comes to transmitting data to your router, you might be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Tips for Apple macOS / OSX Users
Regardless of whether you are using OSX or macOS versions such as 10.11.9, 11.4.5, or 12.1.1, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a set of correlated values over time, making automated remote troubleshooting essential. This is particularly useful for teams that have embraced remote work and Work From Anywhere (WFA).
Pre-installed Scripts for Assistance
A useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of the current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting. In addition, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is related to wireless settings and is only point-in-time, similar to wdutil.
To run it in the background and have it write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, use the command sudo /usr/bin/sysdiagnose but be aware that it 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 about 300MB on average.
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