How To DiagnOSe MacOS Internet Connection
Understanding the Functioning of Internet Addressing
When using the Internet, individuals can be assigned Public IPv4 addresses such as 236.212.23.165 and IPv6 addresses like 2000:f3bd:44f7:899f:120c:6bfe:8caf:f8cc. The verification of these addresses can be done at https://test-ipv6.com/. Nevertheless, attempting to communicate these addresses, or even mentioning MAC addresses like dd:bd:5b:0a:a2:0c can be prone to errors and complicates matters further. Moreover, it does not provide any historical data, particularly when referring to past issues.
Navigating the World Wide Web
When accessing a website like https://romaguera.info, the initial step involves contacting a DNS server to translate the host section (romaguera) in combination with the Top Level Domain (info) of the URL into an IP address, such as 208.166.129.230. With every web request, your computer and browser disclose their types, e.g. Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
Understanding the Significance of Default Gateways
The default gateway is usually an address that is automatically configured through DHCP. A default gateway, such as 172.19.98.77 (typically ending in .1 or .254 based on the scope size) is where all the traffic from your computer is directed to be routed further. For IPv6, a detailed explanation can be found in the how-to-fix-ipv6-connectivity/ article. On Mac or Linux, this can be verified with:
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 172.19.98.77 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 fe80:740:ac68:ad5f:7b6a%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): {78.109.242.246, 138.102.208.49}
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 dd:bd:5b:0a:a2:0c
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 a1:34:45:a1:c0:56
}
Solutions for Connectivity Issues
When it comes to transferring data to your router, it’s essential to troubleshoot issues with both wired and wireless (Wi-Fi) mediums at the physical and data layer.
Tips for Resolving Problems on Apple macOS / OSX
Regardless of whether you’re using OSX or macOS, be it version 10.13.8, 11.3.8, or 12.2.3, 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 invaluable, especially for teams that are committed to remote work and Work From Anywhere (WFA).
Useful Built-in Tools
On OSX/macOS, the sudo wdutil info tool is extremely beneficial as it provides a dump of current wireless settings to the CLI, and can also be set up to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to produce a wide range of logs, although some are only related to wireless settings at a specific point in time, much like wdutil.
To run sysdiagnose in the background and generate logs in /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. Alternatively, for an interactive (albeit limited) experience, run sudo /usr/bin/sysdiagnose and follow the privacy warning. When not run in the background, Finder should open in the correct location, or use Cmd+Shift+G in Finder to navigate to /var/tmp and beware of file sizes of approximately 300MB.
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