How Can I DiagnOSe MacOS Connectivity
Understanding How Internet Addressing Functions
When using the Internet, you may be assigned a Public IPv4 address such as 207.169.140.2 or an IPv6 address, for example 2000:6284:3fcb:9416:4679:9b84:5fe3:8ae4. You can verify this information by visiting https://test-ipv6.com/. Communicating these addresses, or even referencing MAC addresses like fb:6c:f5:1b:e4:e2, can become cumbersome and error-prone, especially for individuals with limited technical knowledge. Moreover, it fails to provide any historical data, particularly in cases where previous issues have arisen.
Navigating the Web
Accessing a webpage, such as https://conroy-dach.io, involves initially reaching out to a DNS server in order to convert the host portion (conroy-dach) in combination with the Top Level Domain (io) of the URL to an IP address, for instance 78.222.135.137. Whenever your computer and browser send out web requests, they include details about the type, for example: Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
The Significance of Default Gateways
The default gateway is typically an address that is automatically configured through DHCP. It usually takes the form of a default gateway such as 192.0.0.13 (although they typically end in .1 or .254 depending on the scope size), and this is the point where your computer directs all of its traffic for routing purposes. For IPv6, there is comprehensive information available in our blog post titled how-to-fix-ipv6-connectivity/. Mac or Linux users can check this information using the following method:
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 192.0.0.13 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 fe80:6098:912:f62f:5c1b%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): {35.45.255.2, 53.75.114.217}
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 fb:6c:f5:1b:e4:e2
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 db:09:ef:81:2b:29
}
Fixing Issues with Wired and Wireless Connections
When it comes to transferring data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting on Apple’s macOS / OSX Operating Systems
No matter which version of OSX/macOS you are currently using - whether it’s 10.15.6, 11.3.7, or 12.0.2 - there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes especially useful, particularly for teams that practice remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts for Assistance
One particularly useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless-related settings in the CLI, and can also be configured to generate specific logs for troubleshooting purposes. Moreover, the sysdiagnose tool can be used to generate a wide array of logs, although many of them are only applicable to wireless issues, similar to wdutil.
To run it 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, but be cautious of the large file sizes, roughly around 300MB.
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