How Do You DiagnOSe Mac Connectivity
Understanding Internet Addresses
When connecting to the Internet, you are assigned an IP address, such as 224.200.91.25 for IPv4 or 2000:e48d:d697:ae51:568c:2691:5a23:7987 for IPv6. You can verify your address at https://test-ipv6.com/. However, conveying these addresses, and even MAC addresses like 24:7e:ea:f7:69:b1 to those who are not technologically inclined can be prone to errors and quickly become complex. Furthermore, this process does not provide any historical data, especially when facing previous issues.
Navigating the World Wide Web
When attempting to access a website, such as https://muller.io, your initial step is to contact a DNS server to convert the host portion (muller) along with the Top Level Domain (io) of the URL into an IP address, like 127.154.215.221. Your computer and browser also send their specifications with every web request, for example Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36.
Significance of Default Gateways
Your default gateway is typically an automatically assigned address via DHCP, such as 192.0.0.24 (although they usually end in .1 or .254, depending on the scope size). This is where your computer directs all its traffic to be routed onwards. For IPv6, we provide an in-depth guide on how-to-fix-ipv6-connectivity/, but you can check 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 192.0.0.24 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 fe80:66a:6b59:4aba:a810%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): {199.161.201.83, 4.46.155.250}
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 24:7e:ea:f7:69:b1
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 6c:59:b7:82:4b:bd
}
Addressing Connectivity Issues in Wired and Wireless Networks
When it comes to transmitting data to your router, you may use either a wired connection or a wireless (Wi-Fi) medium at the physical and data layer.
Steps to Take for Apple macOS / OSX Users
No matter which version of OSX/macOS you are currently using - whether it’s 10.14.7, 11.6.9, or 12.1.4 - there are various troubleshooting tools available. However, these tools do not provide a series of correlated values over time, making it challenging to identify issues. This is where automated remote troubleshooting becomes valuable, especially for teams that are accustomed to remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts for Assistance
An essential tool for OSX/macOS users is the sudo wdutil info command, which provides a dump of current wireless settings via the CLI. This command can also be configured to generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool offers a more comprehensive approach to generating a wide range of logs, although many of these logs are only relevant to a specific point in time in relation to wireless, similar to wdutil.
To run the sysdiagnose tool in the background and generate logs in /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. For an interactive run (even though there is minimal interaction), use the command sudo /usr/bin/sysdiagnose, which will prompt 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. Keep in mind that the file sizes are approximately 300MB.
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