How Can I Check MacOS Connectivity
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 236.97.101.161, or an IPv6 address, like 2000:514d:87c8:5f81:b3d1:9512:c237:e388. These addresses can be verified at https://test-ipv6.com/. However, communicating these addresses and MAC addresses, like ac:ff:c3:b8:78:5e, can be challenging for those unfamiliar with technical terminology. Moreover, no historical data is provided, which limits the ability to troubleshoot past issues.
Navigating the World Wide Web
Accessing a website, such as https://labadie-barrows.name, requires an initial connection to a DNS server to translate the URL’s host portion (labadie-barrows) and Top Level Domain (name) to an IP address, such as 180.17.32.4. Furthermore, every web request from your computer and browser includes information about its type, like: Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
The Significance of Default Gateways
The default gateway, typically automatically assigned through DHCP, is an essential element of networking. It is assigned an address, such as 10.187.90.60 (commonly ending in .1 or .254 based on the scope size), and serves as the point where your computer forwards all its traffic. For troubleshooting IPv6 connectivity on Mac or Linux, refer to: how-to-fix-ipv6-connectivity/
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 10.187.90.60 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 fe80:1bea:cf56:cda7:81ee%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): {134.147.49.7, 161.106.192.11}
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 ac:ff:c3:b8:78:5e
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 f1:3a:a0:0d:71:19
}
Troubleshooting Wired and Wireless Networks
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.
Tips for Apple macOS / OSX Users
No matter which version of OSX/macOS you’re using - whether it’s 10.11.2, 11.5.1, or 12.0.8 - there are various troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting comes in handy, especially for teams that are involved in 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 to the CLI of current wireless settings, and can be configured to generate specific logs for troubleshooting purposes. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant to wireless settings, similar to the wdutil tool.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz. Alternatively, you can run sudo /usr/bin/sysdiagnose interactively, which will give 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. Be mindful of the file sizes, which are approximately 300MB.
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