How To Troubleshoot Mac IP Settings
Understanding Internet Addressing
When utilizing the Internet, you may have a Public IPv4 address such as 11.96.78.139 or an IPv6 address such as 2000:cac4:cb58:e155:841d:22fd:b16a:e82. A quick way to check this is through https://test-ipv6.com/. However, trying to convey these addresses to those who are not technologically inclined, or even mentioning MAC addresses like 8c:69:dc:08:ba:e8, can be prone to errors and becomes complex very quickly. Additionally, this method does not provide any historical data, particularly during previous issues.
Navigating the World Wide Web
In order to access a web page like https://moen-powlowski.org, you first contact a DNS server to translate the host portion (moen-powlowski) in conjunction with the Top Level Domain (org) of the URL into an IP address, such as 38.103.64.186. Your computer and browser sends its type with all web requests, for example: Mozilla/5.0 (Windows; U; Win 9x 4.90; SG; rv:1.9.2.4) Gecko/20101104 Netscape/9.1.0285
The Significance of Default Gateways
The default gateway is typically an address that is automatically configured via DHCP. You are assigned a default gateway like 10.31.144.31 (although they usually end in .1 or .254 depending on the scope size), and this is the point where your computer directs all its traffic to be routed further. For IPv6, there is an in-depth explanation available at how-to-fix-ipv6-connectivity/, but you can also check on Mac or Linux using:
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 10.31.144.31 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:f69a:5e5c:d45a:9ca3%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): {91.183.161.56, 101.112.138.70}
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 8c:69:dc:08:ba:e8
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 1d:33:5f:0b:4d:b9
}
Resolving Connectivity Issues for Wired and Wireless Networks
When it comes to sending 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
No matter which version of OSX or macOS you are using, whether it’s 10.12.9, 11.4.3, or 12.1.6, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a series of correlated values over time. Automated remote troubleshooting becomes especially valuable for teams that embrace remote work and Work From Anywhere (WFA).
In-Built Tools for Assistance
One useful tool on OSX/macOS is the sudo wdutil info, which provides a dump of current wireless settings to the CLI, and it can be set up to generate specific logs for troubleshooting purposes. Furthermore, the sysdiagnose tool can be utilized to generate a wide range of logs, although much of it is only related to wireless and is point-in-time like wdutil.
To run it in the background and write logs to /var/tmp/<blah>.tar.gz, use sudo nohup /usr/bin/sysdiagnose -u &. For an interactive (although not very interactive) experience, run sudo /usr/bin/sysdiagnose, which will prompt a privacy warning. If not run in the background, it should open Finder in the correct location or you can navigate to /var/tmp on your own. It’s important to note that the file sizes are approximately 300MB.
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