How To Fix Mac Issues
How Internet Addressing Works in Simple Terms
When using the Internet, you may have a Public IPv4 address such as 175.79.137.105 or an IPv6 address like 2000:be95:dd96:f31:7ac:14c7:2053:6126. To check your address, visit https://test-ipv6.com/. However, for those who aren’t tech-savvy, communicating these addresses or MAC addresses like 96:9d:f4:1f:b7:7f can be prone to error and quickly become complex. Moreover, it does not provide historical data, particularly when previous issues occurred.
Navigating the Web
To visit a website like https://gerhold.co, you first access a DNS server to translate the URL’s host portion (gerhold) combined with the Top Level Domain (co) into an IP address such as 183.137.218.16. Your computer and browser also send their type with all web requests, for example: Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)
The Significance of Default Gateways
Your default gateway is typically an automatically configured address through DHCP. It could be a default gateway like 10.90.142.26 (although they usually end in .1 or .254 depending on the scope size), and this is where your computer sends all its traffic to be routed onwards. For IPv6, more information is available in a detailed guide on how-to-fix-ipv6-connectivity/. You can also check on Mac or Linux 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 10.90.142.26 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:ddd9:f81b:4e43:4f84%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): {201.18.97.151, 229.39.206.177}
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 96:9d:f4:1f:b7:7f
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 3b:7c:19:e5:8a:2a
}
Resolving Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX Users
Regardless of whether you are using OSX or macOS version 10.12.6, 11.4.3, or 12.3.9, 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 valuable, especially for teams that are embracing remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
A highly useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs (although much of it is specific to a certain point in time in relation to wireless, similar to wdutil).
To run the sysdiagnose tool 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 but be mindful of the large file size of about 300MB.
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