How Can I Check Mac Connectivity
Understanding Internet Addressing
When using the Internet, you are assigned a unique public address, such as IPv4 address 237.124.70.148 or an IPv6 address like 2000:9fa1:a650:59bf:f9e2:cbb7:a726:8e77. The website https://test-ipv6.com/ can be used to verify these addresses. However, for those who are not familiar with technical jargon, communicating or even recognizing these addresses, or MAC addresses like ad:ce:a3:76:32:2f, can be prone to errors and quickly become complex. Furthermore, this method does not provide historical data, especially for past issues.
Navigating the World Wide Web
When attempting to access a webpage such as https://wolff.co, your initial step is to contact a DNS server to convert the host section (wolff) combined with the Top Level Domain (co) to an IP address, such as 139.163.99.154. Additionally, your computer and browser transmit their specifications with each web request, for example:
Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
The Significance of Default Gateways
Your default gateway is typically an address configured automatically through DHCP. This gateway, such as 172.26.91.98 (usually ending in .1 or .254 based on the scope size), is where your computer directs all its traffic to be forwarded. For a detailed explanation on IPv6, please refer to how-to-fix-ipv6-connectivity/. On Mac or Linux systems, this can be verified using the following command:
ifconfig
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 172.26.91.98 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:b198:e90:e294:c596%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): {105.179.24.197, 88.233.107.236}
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 ad:ce:a3:76:32:2f
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 e6:c1:16:20:1c:c5
}
Resolve Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you might be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
No matter which version of OSX/macOS you are currently using - whether it’s 10.11.8, 11.6.8, or 12.0.2 - there are various tools available for resolving issues. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes essential, especially for teams that have adopted remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One of the most helpful tools on OSX/macOS is the sudo wdutil info, which provides a dump of the current wireless settings to the CLI and can be configured to generate specific troubleshooting logs. Additionally, the sysdiagnose tool can generate a wide range of logs, although much of it is only relevant to wireless issues, similar to wdutil.
To run the sysdiagnose in the background and generate logs in /var/tmp/<blah>.tar.gz, you can use the command: sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, 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 manually navigate to /var/tmp using Finder with Cmd+Shift+G. Keep in mind that the file sizes are approximately 300MB.
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