How Can I Understand Mac Issues
Understanding the Function of Internet Addressing
The Internet utilizes distinct types of IP addresses, such as the Public IPv4 11.201.24.208 and the IPv6 address 2000:4f54:1870:a98f:2305:470f:49a6:5194. You can verify this information by visiting https://test-ipv6.com/. However, conveying these addresses to individuals who are not tech-savvy or even referencing MAC addresses like 65:cf:01:9a:1c:dc can lead to errors and complexity. Furthermore, this method does not provide historical data, particularly for past issues.
Navigating the Internet
Accessing a website like https://leffler-batz.net initially involves interacting with a DNS server to convert the host portion (leffler-batz) combined with the Top Level Domain (net) of the URL into an IP address, such as 68.41.50.37. Your computer and browser includes its type in all web requests, 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
Significance of Default Gateways
The default gateway is usually a automatically assigned address through DHCP. This results in obtaining a default gateway like 192.168.6.119 (typically ending in .1 or .254 depending on the scope size), which serves as the destination for all traffic from your computer to be routed onwards. For IPv6, you can explore this further on how-to-fix-ipv6-connectivity/ or check 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 192.168.6.119 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:f9e1:5490:63c2:f269%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): {27.8.181.92, 72.116.241.119}
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 65:cf:01:9a:1c:dc
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 76:6c:66:41:0b:4c
}
Resolving Network Connectivity Issues for Wired and Wireless Connections
When it comes to transmitting data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Solutions for Apple macOS / OSX Users
Irrespective of your OSX/macOS version, be it 10.13.2, 11.2.2, or 12.1.7, there are various troubleshooting tools available. However, the manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting proves to be beneficial, especially for teams that have embraced remote work and Work From Anywhere (WFA) culture.
Useful In-built Scripts
One beneficial tool for OSX/macOS users is sudo wdutil info, which provides a dump to the CLI of current wireless settings and can also be configured to generate specific troubleshooting logs. Another option is the sysdiagnose tool, which can generate a wide range of logs related to wireless (though many are only relevant at a specific point in time, similar to wdutil).
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will create logs in /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively, you can execute sudo /usr/bin/sysdiagnose and it will display 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 approximately 300MB.
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