How To Troubleshoot Mac Connectivity
Understanding IP Addressing
When using the Internet, you are assigned a Public IPv4 address such as 130.171.200.42 or an IPv6 address like 2000:44cf:5d3d:22d7:df1f:eb81:c17c:1f2b. You can verify this information by visiting https://test-ipv6.com/. However, for those who are not technically inclined, conveying and working with these addresses, or even mentioning MAC addresses like a8:49:62:93:26:ea, can be prone to mistakes and can become complex. Moreover, this approach does not provide any historical data, particularly when dealing with past issues.
Navigating the Internet
When attempting to access a website such as https://tremblay.info, the first step involves reaching a DNS server to convert the host segment (tremblay) in combination with the Top Level Domain (info) of the URL into an IP address like 14.47.251.62. During all web requests, your computer and browser actually sends its own type, for example:Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A
Understanding the Significance of Default Gateways
The default gateway is typically an automatically configured address via DHCP. You are provided with a default gateway such as 192.168.31.167 (usually ending in .1 or .254 based on the scope size), and this is where your computer directs all its traffic to be routed to. For IPv6, a detailed explanation is available at how-to-fix-ipv6-connectivity/, and you can also verify this 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 192.168.31.167 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:ebd1:d740:8c86:ffbe%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): {63.132.133.54, 84.6.139.43}
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 a8:49:62:93:26:ea
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 d3:5a:7f:e9:80:56
}
Solutions for Fixing Connectivity Issues
When it comes to transferring data to your router, you may encounter issues at the physical and data layer, especially if you are using a wired or wireless (Wi-Fi) medium.
Resolving Problems on Apple Devices
Regardless of the version of OSX/macOS you are using, whether it’s 10.15.8, 11.5.1, or 12.0.5, there are various troubleshooting tools available. However, these manual actions and scripts may not provide a complete series of correlated values over time, which is a limitation. This is where automated remote troubleshooting becomes valuable, particularly for teams that are embracing remote work and Work From Anywhere (WFA).
Leveraging Built-in Tools for Assistance
One of the helpful tools on OSX/macOS is the sudo wdutil info, which provides a dump to the CLI of current wireless settings. This tool can also be configured to generate specific logs for troubleshooting purposes. Additionally, the sysdiagnose tool offers a more comprehensive approach by generating a wide array of logs, although many are only point-in-time related to wireless, similar to wdutil.
To run the sysdiagnose tool in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run the tool interactively, use sudo /usr/bin/sysdiagnose and be prepared for 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. Keep in mind that the file sizes are around 300MB more or less.
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