How To Understand Mac Issues
Understanding Internet Protocol Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 111.94.143.84, or an IPv6 address like 2000:eeac:dc8d:db8c:523b:d903:4d12:df75. You can verify your assigned address by visiting https://test-ipv6.com/. However, conveying these addresses to individuals without technical knowledge, or even referencing MAC addresses like 83:3a:47:66:43:cd, can be prone to mistakes and quickly become complex. Moreover, this method does not provide any historical data, especially for past issues.
Navigating the World Wide Web
When accessing a website like https://beier-green.name, your device initially contacts a DNS server to translate the host portion (beier-green) along with the Top Level Domain (name) of the URL into an IP address, such as 28.62.100.210. For all web requests, your computer and browser will send specific information, such as: Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
The Significance of Default Gateways
Normally, your default gateway is automatically configured through DHCP and is assigned an address, such as 10.252.13.249 (although they typically end in .1 or .254 depending on the scope size). This is the point where your computer directs all its traffic to be routed onwards. To learn more about IPv6, you can refer to our in-depth guide on how-to-fix-ipv6-connectivity/. On Mac or Linux systems, you can verify this information using the following command:
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 10.252.13.249 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:e6c3:241b:85f3:fc32%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): {15.127.234.118, 22.119.185.66}
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 83:3a:47:66:43:cd
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 0c:e2:13:dd:f9:2c
}
Fixing Connection Issues for Wired and Wireless Networks
When it comes to transmitting data, you have the option to use a wired or wireless (Wi-Fi) medium at the physical and data layer to send the data to your router.
Troubleshooting Tips for Apple macOS / OSX
Regardless of whether you are using OSX or macOS, whether it’s version 10.12.9, 11.2.5, or 12.1.9, there are various tools available for troubleshooting. However, manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes crucial, especially for teams that embrace remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One valuable tool in OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless related settings to the CLI. It can also be configured to generate specific logs for troubleshooting. In addition, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is related to wireless settings and is point-in-time only, 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, you can use sudo /usr/bin/sysdiagnose. 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 around 300MB.
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