Troubleshoot OSX IP Settings
An Overview of Internet Addressing
When you are connected to the Internet, you will be assigned a Public IPv4 address, such as 175.146.158.181, or an IPv6 address, like 2000:2c79:19e7:8885:e9f7:2754:486e:e75a. You can easily verify this information through the use of a website like https://test-ipv6.com/. However, attempting to communicate these addresses to individuals who are not technologically-savvy can be error-prone and complex, not to mention the lack of historical data, especially when prior issues arose.
The Process of Navigating the Web
Accessing a web page, such as https://bayer.io, involves an initial interaction with the DNS server, which translates the host portion (bayer) combined with the Top Level Domain (io) of the URL into an IP address, such as 205.45.189.56. Remarkably, your computer and browser include specific information with all web requests, for instance, Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16.
Understanding the Role of Default Gateways
Your default gateway is typically an address that is automatically configured via DHCP. It serves as the destination for all outgoing network traffic from your computer before being routed onwards. For IPv6, detailed instructions can be found in our blog post titled how-to-fix-ipv6-connectivity/, but you can also perform a 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 192.0.0.230 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 fe80:8d62:7440:d805:56d0%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): {94.47.168.77, 30.77.169.181}
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 a7:a5:a1:49:90:3d
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 86:98:81:2c:a4:eb
}
Resolving Issues with Wired and Wireless Connectivity
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 Solutions for Apple macOS / OSX
Regardless of the version of OSX/macOS you are using, whether it’s 10.14.3, 11.4.5, or 12.3.1, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes extremely valuable, especially for teams that adopt remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts for Assistance
One valuable tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI, and it can also be configured 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 relevant to wireless at a specific point in time, similar to wdutil.
To run sysdiagnose in the background and have it 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 (even though there is minimal interaction), you can use sudo /usr/bin/sysdiagnose, which will prompt 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. It’s important to note that the file sizes are approximately 300MB.
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