How Can I DiagnOSe Mac Internet Connection
Understanding Internet Addressing
When using the Internet, you are assigned a unique Public IPv4 address such as 44.191.14.43 or an IPv6 address like 2000:3e1:c69c:c907:e9b:18b6:2888:159. You can verify your address by visiting https://test-ipv6.com/. However, explaining or transmitting these addresses, along with MAC addresses like 30:bb:52:02:cd:eb, can be challenging for those not well-versed in technology. This also lacks historical data, especially regarding past issues.
Navigating the World Wide Web
To access a website like https://osinski-cartwright.co, your computer first consults a DNS server to translate the host portion (osinski-cartwright) combined with the Top Level Domain (co) of the URL into an IP address, such as 108.112.146.132. Your computer and browser send their type with all web requests, for example: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
Significance of Default Gateways
The default gateway is typically an automatically configured address through DHCP, such as 10.251.220.24 (although they usually end in .1 or .254 depending on the scope size). This is the point to which your computer sends all its traffic to be routed further. For IPv6, detailed guidance can be found at how-to-fix-ipv6-connectivity/, and 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 10.251.220.24 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:cb3e:351c:59cb:1077%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): {249.224.99.61, 67.162.29.250}
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 30:bb:52:02:cd: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 ac:5e:6d:ac:f3:5e
}
Resolving Connectivity Issues: Wired vs Wireless
When it comes to sending data to your router, you may be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Solutions for Apple macOS / OSX
No matter which version of OSX/macOS you have - whether it’s 10.14.1, 11.3.6, or 12.1.4, there are various tools available for resolving connectivity issues. However, manual actions and scripts alone do not provide a series of correlated values over time. This is where automated remote troubleshooting proves to be especially beneficial, particularly for teams that embrace remote work and Work From Anywhere (WFA).
Utilizing Pre-installed Scripts for Assistance
A very useful tool available on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI and can also be configured to generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool offers a more comprehensive approach by generating a wide range of logs (although most are point-in-time related to wireless, similar to wdutil).
To run the 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, which will provide a privacy warning. When 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 usually around 300MB.
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