How Can I Troubleshoot MacOS Connectivity
The Functioning of Internet Addressing
When using the Internet, individuals may have a Public IPv4 address, such as 75.129.175.54, or an IPv6 address, like 2000:4aec:dc44:e9ed:4118:3d75:40cf:f8e4. These addresses can be verified at https://test-ipv6.com/. However, communicating these addresses, and even MAC addresses like 0a:ea:a5:f1:0f:c7, can be error-prone and quickly become complex, especially for those who are not technically inclined. Furthermore, this method does not provide any historical data, particularly from previous issues.
Navigating the Internet
When attempting to visit a webpage like https://feil.co, the first step is to access a DNS server in order to translate the host portion (feil) combined with the Top Level Domain (co) of the URL into an IP address, such as 242.15.177.112. As your computer and browser send their type with all web requests, for example, Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
The Significance of Default Gateways
Typically, the default gateway is an automatically configured address via DHCP, such as 192.0.0.140 (although they typically end in .1 or .254, depending on the scope size). This is the location where your computer sends all traffic to be routed onward. For IPv6, a comprehensive guide can be found at how-to-fix-ipv6-connectivity/, and on Mac or Linux, it can be checked by:
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 192.0.0.140 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 fe80:3769:a93c:760:8418%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): {24.43.99.161, 65.146.217.228}
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 0a:ea:a5:f1:0f:c7
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 ee:a9:be:e3:5c:ba
}
Resolve Issues with Wired and Wireless Networks
When it comes to sending data to your router, you may be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of the version of OSX/macOS you are using, whether it’s 10.12.5, 11.5.3, or 12.2.8, there are a variety of tools available for resolving issues. However, these tools and manual actions do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes valuable, particularly for teams that embrace remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
On OSX/macOS, the sudo wdutil info tool is very helpful as it provides a dump of current wireless settings to the command line interface and can also generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only point-in-time information related to wireless, similar to wdutil.
To run sudo nohup /usr/bin/sysdiagnose -u & in the background and write logs to /var/tmp/<blah>.tar.gz, or run sudo /usr/bin/sysdiagnose interactively, keeping in mind that the file sizes are approximately 300MB more or less.
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