DiagnOSe Apple Internet Connection
Understanding Internet Addressing
When it comes to the Internet, you are assigned either a Public IPv4 or IPv6 address. You can easily check your address by visiting https://test-ipv6.com/. However, explaining or referencing these addresses, as well as MAC addresses, can quickly become complex and error-prone, especially for those who are not tech-savvy. Moreover, this method does not provide any historical data, which is particularly important when troubleshooting past issues.
Navigating the World Wide Web
When you want to visit a website, such as https://schmidt.io, your computer first contacts a DNS server to convert the URL into an IP address. For example, the host portion “schmidt” combined with the Top Level Domain “io” is translated into an IP address like 228.226.81.98. It’s important to note that your computer and browser also send specific information with every web request, such as the user agent string:
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
Your default gateway is typically assigned automatically through DHCP and acts as the central routing point for all your computer’s outgoing traffic. This gateway is usually in the form of an address like 192.168.64.29, ending in .1 or .254 depending on the scope size. For more information on configuring default gateways for IPv6, you can refer to our in-depth guide at how-to-fix-ipv6-connectivity/. Additionally, you can verify default gateways on Mac or Linux using:
command to verify default gateways
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 192.168.64.29 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 fe80:406:6c0c:d2d7:96f9%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): {174.110.146.177, 239.5.201.128}
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 76:e7:c2:6e:c3:34
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 51:a6:29:9e:e2:47
}
Resolving Connection Issues for Wired or Wireless Networks
When it comes to transmitting data to your router, you might be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Techniques for Apple macOS / OSX
Regardless of whether you are using OSX/macOS versions such as 10.13.6, 11.5.1, or 12.1.1, there are various tools available for troubleshooting. However, these manual methods and scripts do not provide a set of correlated values over time, which is where automated remote troubleshooting becomes essential, especially for teams embracing remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting. Additionally, the comprehensive sysdiagnose tool can be used to generate a wide range of logs, although it is mostly point-in-time in relation to wireless, much like wdutil.
To run sudo nohup /usr/bin/sysdiagnose -u & in the background and write logs to /var/tmp/<blah>.tar.gz, or to run it interactively, use 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 it can be navigated to using /var/tmp or Finder with Cmd+Shift+G, bearing in mind the file sizes of about 300MB more or less.
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