How To Troubleshoot OSX IP Settings
Understanding Internet Protocol Addressing
When using the Internet, you will be assigned a Public IPv4 address, such as 81.28.117.36, or an IPv6 address like 2000:1cf4:2b0f:1dad:59d3:8bae:dc6:9793. You can verify this information by visiting https://test-ipv6.com/. However, for individuals who are not well-versed in technology, attempting to convey or identify these addresses, including MAC addresses like fa:85:83:19:59:7d, can lead to errors and become complicated. Furthermore, this method does not provide any historical data, especially regarding previous issues.
Navigating the World Wide Web
When accessing a webpage such as https://morar.org, you first connect to a DNS server to convert the host part (morar) combined with the Top Level Domain (org) of the URL into an IP address like 202.72.167.7. Your computer and browser also include its type in all web requests, for example: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A.
The Significance of Default Gateways
In most cases, your default gateway is an address that is automatically configured via DHCP. You are typically assigned a default gateway like 192.0.0.64 (although they generally end in .1 or .254 based on the size of the scope). This is the point where your computer directs all its traffic to be routed further. For IPv6, detailed instructions are available at how-to-fix-ipv6-connectivity/, but on Mac or Linux systems, it can be verified with:
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 192.0.0.64 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 fe80:5a8c:11b3:2edf:60bd%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): {19.108.50.223, 237.90.56.117}
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 fa:85:83:19:59:7d
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 20:dd:87:89:c8:76
}
Resolving Connectivity Issues with Wired and Wireless Networks
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 Devices
No matter which version of OSX/macOS you are currently using - whether it’s 10.15.9, 11.2.7, or 12.1.6 - there are a variety of 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 proves to be particularly useful, especially for teams that are embracing remote work and Work From Anywhere (WFA).
Utilizing In-Built Scripts for Assistance
A very useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless related settings to the CLI and can also be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only related to wireless settings at a specific point in time, 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 (even though there’s not much interaction), you can run sudo /usr/bin/sysdiagnose and it will give you 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 point it to the path. However, be aware of the file sizes, which are approximately 300MB more or less.
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