How Do You Troubleshoot Mac IP Settings
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 212.54.174.184, or an IPv6 address, like 2000:b9e1:6ec6:ff0c:346b:a404:9b51:e0fb. You can verify these addresses on https://test-ipv6.com/. However, conveying these addresses, or even MAC addresses like d8:42:08:44:53:29, to individuals who are not technologically savvy can be prone to errors and can become complex. This method also does not provide historical data, especially when previous issues occurred.
Navigating the World Wide Web
When accessing a web page, such as https://parker.net, you first connect to a DNS server to convert the host portion (parker) combined with the Top Level Domain (net) of the URL to an IP address, like 189.121.118.85. Your computer and browser send their type with all web requests, for example: Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
The Significance of Default Gateways
Your default gateway is typically an automatically configured address via DHCP. You are assigned a default gateway, such as 172.26.150.213 (although they typically end in .1 or .254 depending upon the scope size), and this is where your computer sends all of its traffic to be routed onwards. For IPv6, you can delve deeper into this topic by visiting how-to-fix-ipv6-connectivity/, and you can verify on Mac or Linux systems using the following command:
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 172.26.150.213 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 fe80:1db:9b77:9d77:3242%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): {30.103.45.222, 92.143.213.108}
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 d8:42:08:44:53:29
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 11:5d:d7:53:dc:39
}
Resolving Issues with Wired and Wireless Connections
When it comes to sending data to your router, you might be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Tips for Apple macOS / OSX Users
No matter which version of OSX/macOS - be it 10.15.8, 11.6.1, or 12.0.8 - there are several troubleshooting tools available for you. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes essential, especially for teams that are embracing remote work and the concept of Work From Anywhere (WFA).
Useful Built-in Scripts
One tool that you can use on OSX/macOS is sudo wdutil info, which provides a dump of current wireless 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.
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 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 Cmd+Shift+G in Finder. Keep in mind that the file sizes are approximately 300MB.
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