Troubleshoot MacOS IP Settings
Explanation of Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 48.245.48.64, or an IPv6 address, such as 2000:e94e:e078:97b:3468:c6ef:d9aa:4df5. You can verify this information by visiting https://test-ipv6.com/. However, sharing and communicating these addresses, as well as MAC addresses like 20:b4:1f:1e:97:8f, can be prone to errors and become complex for those who are not technologically-inclined. Additionally, this method does not provide any historical data, especially relating to past issues.
Navigating the World Wide Web
In order to access a web page, such as https://funk-marks.name, your computer must first communicate with a DNS server to convert the host portion (funk-marks) and the Top Level Domain (name) of the URL into an IP address, like 52.70.143.133. When making web requests, your computer and browser also send its specifications, for example:
Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
Understanding the Significance of Default Gateways
Your default gateway is generally assigned automatically through DHCP. It is usually an address ending in either .1 or .254, depending on the scope size, for instance: 192.168.82.34. This is the designated point where your computer directs all its traffic to be further routed. For information on checking IPv6 on Mac or Linux, you can refer to our comprehensive guide: how-to-fix-ipv6-connectivity/
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 192.168.82.34 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 fe80:9ec9:82e9:238f:8dda%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): {228.51.87.188, 244.164.240.157}
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 20:b4:1f:1e:97:8f
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 c7:9e:07:9a:12:10
}
Resolving Connectivity Issues for Wired or Wireless Networks
When it comes to transmitting data to your router, you may be utilizing a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX Users
Irrespective of the version of OSX/macOS you are using, whether it’s 10.15.7, 11.0.8, or 12.0.9, there are various tools available for resolving connectivity problems. However, these tools do not provide a series of correlated values over time, which is essential for effective troubleshooting. This is where automated remote troubleshooting becomes invaluable, especially for teams operating remotely and embracing the concept of Work From Anywhere (WFA).
Utilizing Built-in Scripts for Troubleshooting
One extremely useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of the current wireless-related settings in the Command Line Interface (CLI). This command can also be configured to generate specific logs for troubleshooting purposes. Additionally, the more comprehensive sysdiagnose tool can generate a wide range of logs, although much of it is only point-in-time data in relation to wireless, similar to wdutil.
Running the command sudo nohup /usr/bin/sysdiagnose -u & in the background will write the logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively, you can execute sudo /usr/bin/sysdiagnose, which will provide 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 to point Finder to the path. However, be cautious of the file sizes, which are approximately 300MB.
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