Fix Mac Internet
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 139.206.205.234, or an IPv6 address, like 2000:3bbf:d47e:84f1:d023:6a4d:c68b:ce9c. You can verify your address by visiting https://test-ipv6.com/. However, for those who are not well-versed in technology, communicating these addresses, or even identifying MAC addresses like 7a:44:cd:3f:18:bb, can be error-prone and quickly become complex. Moreover, this method does not provide historical data, especially for past issues.
Navigating the World Wide Web
Accessing a website, such as https://ankunding.name, involves initially connecting to a DNS server to convert the host portion (ankunding) in combination with the Top Level Domain (name) of the URL to an IP address, such as 121.70.20.166. Your computer and browser send their specifications with 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
Understanding the Significance of Default Gateways
The default gateway is typically an automatically assigned address through DHCP. You are provided with a default gateway, such as 10.35.4.242 (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 onward. For IPv6, a comprehensive guide on how-to-fix-ipv6-connectivity/ is available, but you can also verify this 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 10.35.4.242 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 fe80:923e:3e10:fb07:97bc%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): {253.89.43.166, 99.205.105.231}
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 7a:44:cd:3f:18:bb
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 e8:36:54:f2:34:04
}
Resolving Issues with Wired and Wireless Connections
When it comes to transferring data to your router, you may be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of whether you are using OSX/macOS versions such as 10.14.2, 11.5.9, or 12.1.9, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes essential, especially for teams that are embracing remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One 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 point-in-time related to wireless, similar to wdutil).
To run the sysdiagnose tool in the background and write logs to /var/tmp/<blah>.tar.gz, you can use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can use the command sudo /usr/bin/sysdiagnose, which will provide 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. However, be cautious of the file sizes, which are approximately 300MB or slightly more.
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