How To Support MacOS Internet Connection
Understanding Internet Addressing
When using the Internet, you are assigned a unique Public IPv4 or IPv6 address. You can check your IP address at https://test-ipv6.com/, but communicating and managing these addresses can be complex for non-technical users. Obtaining historical data for previous issues can also be challenging.
Navigating the World Wide Web
Accessing a website like https://hyatt.net involves translating the website’s URL to an IP address using a DNS server. Your computer and browser also share important data with each web request, such as the type and version.
Significance of Default Gateways
The default gateway, usually assigned via DHCP, is the designated route for all outgoing traffic from your computer. This is typically an address like 172.23.40.115, ending in .1 or .254 based on the network scope. For IPv6, detailed troubleshooting steps are available at how-to-fix-ipv6-connectivity/, and instructions for Mac or Linux users are provided.
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 172.23.40.115 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 fe80:3cf4:c74:af47:6582%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): {208.87.169.136, 71.17.224.255}
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 62:8b:fc:d7:17:ab
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 96:a4:65:d9:52:54
}
Fixing Connection Issues for Wired and Wireless Networks
When sending data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Resolving Connectivity Problems on Apple macOS / OSX
Irrespective of the version of OSX/macOS you are using, whether it’s 10.13.6, 11.1.9, or 12.0.1, there are various troubleshooting tools available. However, the manual actions and scripts don’t provide a series of correlated values over time. This is where automated remote troubleshooting becomes essential, particularly for teams that adopt remote work and Work From Anywhere (WFA).
Utilizing Internal Scripts for Assistance
One useful tool on OSX/macOS is the sudo wdutil info, which provides a dump of current wireless settings to the CLI, and can also be configured to generate specific logs for troubleshooting. Another comprehensive tool is the sysdiagnose tool, which can be used to generate a wide range of logs, although much of it pertains to wireless settings just like wdutil.
To run it in the background and write logs to /var/tmp/<blah>.tar.gz, you can use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, use the command sudo /usr/bin/sysdiagnose, but beware of the large file sizes of about 300MB.
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