How Do You Test OSX Connectivity
The Functioning of Internet Addressing
When using the Internet, you may be assigned a Public IPv4 address, for example 26.255.217.101, or an IPv6 address like 2000:c275:be6d:d170:ccf0:dde5:dbf7:c621. You can verify this information by visiting https://test-ipv6.com/. However, for those not well-versed in technology, communicating these addresses or even referring to MAC addresses like 1d:32:72:ab:f9:dd, can be prone to errors and can become complex quickly. Moreover, this method does not offer any historical data, particularly from past issues.
Navigating the Internet
To access a webpage such as https://flatley.info, you begin by connecting to a DNS server to convert the host segment (flatley) and the Top Level Domain (info) of the URL into an IP address, such as 135.216.94.219. Your computer and browser send their type with each web request, for example Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
Understanding the Significance of Default Gateways
Typically, your default gateway is an address that is automatically configured through DHCP. You receive a default gateway, such as 172.16.23.252 (although they usually end in .1 or .254 depending on the size of the scope), and this is where your computer sends all of its traffic to be routed forward. For IPv6, we offer an extensive guide on how-to-fix-ipv6-connectivity/, but you can verify 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 172.16.23.252 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 fe80:7d60:d009:29cd:f33%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): {55.124.48.181, 216.220.250.74}
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 1d:32:72:ab:f9:dd
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 c4:66:7f:16:05:b1
}
Solutions for Resolving Issues with Wired or Wireless Network Connections
When it comes to transmitting data to your router, you may be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Tips for Resolving Problems on Apple’s macOS / OSX Operating System
No matter which version of OSX/macOS you are currently using, whether it’s 10.14.8, 11.1.4, or 12.2.1, there are multiple tools available for troubleshooting. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes incredibly useful, particularly for teams that have embraced remote work and the Work From Anywhere (WFA) concept.
Useful Built-in Scripts for Troubleshooting
One valuable 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 the information is only relevant to wireless settings, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & will execute the tool in the background and write logs to /var/tmp/<blah>.tar.gz. For those who prefer to run it interactively, the command sudo /usr/bin/sysdiagnose can be used, with a privacy warning provided. When not run in the background, it should open Finder in the correct location or users can navigate to /var/tmp using Finder with Cmd+Shift+G. However, be cautious of the file sizes, which are typically around 300MB.
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