How Do You Understand Mac Issues
The Basics of Internet Addressing
When using the Internet, you will be assigned a Public IPv4 address such as 50.113.123.74 or an IPv6 address like 2000:ee47:ff11:3206:511a:a0c7:29cd:3954. You can verify this at https://test-ipv6.com/. However, explaining or communicating these addresses, as well as MAC addresses like 2f:b6:fe:7d:1d:1f, can be prone to errors and become complex. Moreover, it lacks historical data, especially for previous issues.
Navigating the World Wide Web
In order to reach a website such as https://denesik.biz, you first need to access a DNS server to convert the host portion (denesik) combined with the Top Level Domain (biz) of the URL to an IP address like 3.64.169.135. Whenever your computer and browser make web requests, they actually include their 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
Typically configured automatically through DHCP, your default gateway is an essential part of your network. It usually appears in the form of an address like 172.26.63.7 (often ending in .1 or .254 depending on the scope size), and this is where your computer forwards all its traffic to be routed further. For a more in-depth look at IPv6, you can refer to our detailed guide on how-to-fix-ipv6-connectivity/, or check on Mac or Linux with:
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 172.26.63.7 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 fe80:46de:3ae8:762f:9049%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): {97.241.56.137, 155.21.99.5}
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 2f:b6:fe:7d:1d:1f
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 e1:77:b4:e8:8a:30
}
Fixing Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you may be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Strategies for Apple macOS / OSX
Regardless of whether you are running OSX/macOS version 10.13.5, 11.3.6, or 12.2.5, 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 invaluable, particularly for teams that are embracing remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
An incredibly useful tool for OSX/macOS is sudo wdutil info, which provides a dump of the current wireless-related settings in the CLI and can also be configured to generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs, although many of them are point-in-time related to wireless, similar to wdutil.
To run sysdiagnose 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 it interactively, use the command sudo /usr/bin/sysdiagnose and be aware of the large file sizes, typically around 300MB.
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