Understand Mac Internet Connection
Understanding Internet Protocol Addressing
When connecting to the Internet, you are assigned a Public IPv4 address such as 53.29.57.240 or an IPv6 address like 2000:343f:1d17:4f3a:762e:11b:3ba7:8ab. You can verify these addresses on https://test-ipv6.com/. Nevertheless, for individuals who are not well-versed in technology, conveying these addresses, or even identifying MAC addresses like b4:37:bf:f9:ec:eb, can be error-ridden and rapidly become complex. Additionally, this method fails to provide historical data, especially from past issues.
Navigating Through the World Wide Web
To access a website like https://crooks.org, you initially connect to a DNS server to translate the host portion (crooks) along with the Top Level Domain (org) of the URL into an IP address like 216.3.205.44. Your computer and browser transmit its type with every web request, such as Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
The Significance of Default Gateways
The default gateway is typically an address that is automatically configured through DHCP. For instance, you might receive a default gateway like 10.166.175.83 (although they typically end in .1 or .254 depending on the scope size). This is the destination where your computer forwards all its traffic to be routed further. There is also an in-depth exploration of IPv6 connectivity at how-to-fix-ipv6-connectivity/, or you can 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 10.166.175.83 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:bc11:a5e6:fd4:5368%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): {216.196.174.35, 203.6.141.217}
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 b4:37:bf:f9:ec:eb
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 04:b3:14:46:f9:60
}
Resolving Issues with Wired and Wireless Connections
When it comes to sending 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
Regardless of the version of OSX/macOS you are using, whether it’s 10.13.4, 11.5.7, or 12.1.1, there are various tools available for troubleshooting. However, manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes valuable, particularly for teams embracing remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One tool that proves to be very helpful on OSX/macOS is sudo wdutil info, which provides a dump of the current wireless related settings to the CLI and can also 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 only point in time in relation to wireless, similar to wdutil).
To run it in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. Alternatively, if you prefer to run it interactively, you can use sudo /usr/bin/sysdiagnose which will open Finder in the correct location or you can navigate to /var/tmp using Finder with Cmd+Shift+G. Just be mindful of the file sizes, which are typically around 300MB.
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