Troubleshoot Mac Issues
Understanding Internet Addressing
When using the Internet, you will be assigned a Public IPv4 address, such as 91.195.200.96, or an IPv6 address, such as 2000:a604:400b:ad4e:4da3:c9f5:14e3:eb9b. You can verify these addresses at https://test-ipv6.com/. However, for individuals who are not well-versed in technology, communicating these addresses, or even referencing MAC addresses like 37:1c:c4:4e:1e:9d, can be prone to errors and become complex. Additionally, this method does not provide any historical data, especially for past issues.
Navigating the Web
When trying to access a website, such as https://strosin-schoen.name, the first step is to contact a DNS server to convert the host portion (strosin-schoen) in combination with the Top Level Domain (name) of the URL into an IP address, such as 55.201.8.189. Additionally, your computer and web browser include the type of web requests sent with every request, such as Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A
The Significance of Default Gateways
Typically, your default gateway address is configured automatically through DHCP and can be an address like 192.0.0.82 (although they typically end in .1 or .254 depending on the scope size), which is the destination where your computer sends all its traffic to be further routed. For dealing with IPv6, more detailed information is available at how-to-fix-ipv6-connectivity/ but you can verify 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 192.0.0.82 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:d57c:65c0:3863:1134%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): {12.253.118.177, 158.28.232.117}
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 37:1c:c4:4e:1e:9d
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 1e:52:8c:c5:14:71
}
Resolving Connectivity Issues for Wired and Wireless Networks
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 Strategies for Apple macOS / OSX Users
Regardless of whether you are using OSX/macOS versions such as 10.15.2, 11.0.8, or 12.2.6, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes particularly useful, especially for teams that have embraced remote work and the concept of Work From Anywhere (WFA).
Utilizing In-Built Scripts for Assistance
One valuable tool for OSX/macOS users is the sudo wdutil info command, which provides a dump of current wireless-related settings to the CLI and can be configured to generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant to wireless settings at a specific point in time, similar to wdutil.
To run the sysdiagnose tool in the background and generate logs, you can use the command sudo nohup /usr/bin/sysdiagnose -u &, which will write logs to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively, you can use the command sudo /usr/bin/sysdiagnose, although it will display a privacy warning. Running it in this manner should open Finder in the correct location, or you can navigate to /var/tmp using Finder with Cmd+Shift+G. It’s important to be mindful of the file sizes, which are typically around 300MB.
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