How Do You Check OSX Connectivity
Understanding Internet Protocol Addressing
When using the Internet, you are assigned a unique identifier such as 159.92.250.179 for IPv4 or 2000:6cb1:7750:4dff:dd7f:feb7:c086:725 for IPv6. You can verify this information on https://test-ipv6.com/. However, conveying and discussing these addresses, as well as MAC addresses like a5:c8:65:0b:f8:8d, can be prone to errors and become complex. Moreover, it does not provide any historical data, especially for past issues.
Navigating the World Wide Web
To access a website such as https://bernier.name, your device initially communicates with a DNS server to convert the host portion (bernier) along with the Top Level Domain (name) of the URL into an IP address, such as 170.187.192.206. Every web request from your computer and browser contains its type, for example: Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
Significance of Default Gateway Addresses
Your default gateway is typically an automatically assigned address via DHCP. It assigns a default gateway like 10.231.157.91 (commonly ending in .1 or .254 based on the scope size), which serves as the point your computer uses to forward all its traffic. For IPv6, a detailed guide on how-to-fix-ipv6-connectivity/ is available, and you can check it 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 10.231.157.91 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:d5ab:73c9:ad15:5586%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): {156.92.23.141, 110.190.110.41}
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 a5:c8:65:0b:f8:8d
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 43:2d:6a:db:5b:61
}
Resolving Connection Issues for Wired or Wireless Networks
When transmitting data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple’s macOS / OSX Systems
No matter which version of OSX or macOS you are currently operating on - be it 10.13.5, 11.5.5, or 12.0.4 - there are several 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 invaluable, especially for teams that are adopting a remote work and Work From Anywhere (WFA) approach.
Utilizing the In-Built Scripts for Assistance
One useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump to the CLI of the current wireless settings, and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a plethora of logs, though it is primarily point-in-time related to wireless operations, akin to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively, you can execute sudo /usr/bin/sysdiagnose, which will display a privacy warning. When run in the foreground, it should open Finder in the correct location, or you can navigate to /var/tmp. However, be cautious of the file sizes, which are approximately 300MB more or less.
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