How To Test MacOS Connectivity
The Functioning of Internet Addressing
When connected to the Internet, you will receive a unique Public IPv4 address such as 27.70.179.72 or an IPv6 address like 2000:c8e8:2b4e:8477:2593:ea92:5e24:1ae5. You can verify this by visiting https://test-ipv6.com/. However, conveying these addresses or even referencing MAC addresses like 65:e6:0e:ca:d1:6c to those not well-versed in technology can lead to errors and complexity. Furthermore, this method fails to provide any historical data, particularly when recurring issues are involved.
Navigating the Internet
When attempting to access a website such as https://oconnell.name, the first step is to contact a DNS server to convert the host portion (oconnell) in conjunction with the Top Level Domain (name) of the URL to an IP address, such as 45.62.151.0. In all web requests, your computer and browser transmit its type, for instance: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A.
The Significance of Default Gateways
Typically, your default gateway is assigned automatically through DHCP, resulting in a default gateway address such as 10.148.232.227 (often ending in .1 or .254 based on the scope size). This address is where your computer forwards all its traffic to be routed further. For IPv6, you can delve deeply into the topic using how-to-fix-ipv6-connectivity/, but you can also verify it on Mac or Linux by 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 10.148.232.227 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 fe80:8fda:f5a2:bb57:b2b0%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): {165.161.191.15, 143.173.39.237}
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 65:e6:0e:ca:d1:6c
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 54:b2:2e:21:4c:fd
}
Solutions for Resolving Issues with Wired and Wireless Connectivity
When it comes to transmitting data to your router, you may be utilizing a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Techniques for Apple macOS / OSX Users
Regardless of whether you are running OSX/macOS version 10.15.7, 11.5.3, or 12.3.1, there is a variety of tools available for resolving issues. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams that are adapting to remote work and embracing the concept of Work From Anywhere (WFA).
Embedded Scripts for Assistance
A useful tool on OSX/macOS is the sudo wdutil info, which provides a dump of current wireless-related settings to the command-line interface. This can also be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be utilized to generate a wide range of logs, although most of the information is only relevant to wireless connectivity, similar to wdutil.
By running sudo nohup /usr/bin/sysdiagnose -u &, the tool can be executed in the background, and it will write logs to /var/tmp/<blah>.tar.gz for you. If you wish to run it interactively (although there isn’t much interaction involved), you can executesudo /usr/bin/sysdiagnose, which will display a privacy warning. When not run in the background, it should open Finder in the appropriate location, or you can navigate to /var/tmp manually or use Finder with Cmd+Shift+G to locate the path. Keep in mind that the file sizes are approximately 300MB.
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