How Do You Troubleshoot MacOS IP Settings
Functioning of Internet Addressing
When using the Internet, individuals may be assigned a Public IPv4 address such as 31.5.190.150 or an IPv6 address like 2000:ffb7:f2d6:7568:9511:a828:208b:a877. This information can be verified at https://test-ipv6.com/. However, sharing and utilizing these addresses, as well as MAC addresses like ef:63:41:9a:18:ff, can be prone to errors and become complex. Furthermore, it does not provide historical data, especially regarding previous issues.
Navigating the Internet
When accessing a website such as https://mills.co, the process begins with contacting a DNS server to convert the combination of the host portion (mills) and the Top Level Domain (.co) of the URL into an IP address, for example 25.92.146.28. Every web request from your computer and browser includes information about the type, such as Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36.
The Significance of Default Gateways
Typically, a default gateway is an automatically configured address via DHCP. This results in a default gateway address like 10.233.186.211 (commonly ending in .1 or .254 based on the scope size), and it serves as the point to which your computer directs all its traffic for further routing. Detailed guidance on checking for IPv6 connectivity issues can be found at how-to-fix-ipv6-connectivity/ 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 10.233.186.211 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 fe80:8028:b36d:4625:623%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): {16.253.16.14, 245.38.67.152}
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 ef:63:41:9a:18:ff
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 de:4a:e7:b3:75:81
}
Resolving Connectivity Issues for Wired and Wireless Networks
When it comes to transmitting data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of whether you are running OSX/macOS 10.11.8, 11.2.1, or 12.3.7, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams that are embracing remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One 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. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant to wireless at a specific point in time, similar to wdutil.
To run the sysdiagnose tool 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 the command sudo /usr/bin/sysdiagnose, which will trigger 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 Cmd+Shift+G in Finder. Keep in mind that the file sizes will be around 300MB or so.
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