How Do You Understand MacOS Internet
Understanding Internet Addressing
When using the Internet, individuals are assigned either a Public IPv4 address or an IPv6 address. These addresses can be checked using a tool such as https://test-ipv6.com/, but the process of communicating these addresses, and even MAC addresses, can be error-prone and complex, especially for those who are not technically savvy.
Navigating the World Wide Web
Accessing a website, such as https://mitchell.biz, initially involves a request to a DNS server to translate the host and Top Level Domain of the URL into an IP address. Additionally, when making web requests, your computer and browser provide information about their type.
The Significance of Default Gateways
The default gateway, typically obtained through DHCP, serves as the automatic configuration address that your computer sends all its traffic to be routed onwards. For those interested in more detailed information about IPv6 connectivity, a deep dive is available at how-to-fix-ipv6-connectivity/. On Mac or Linux systems, gateway information can be checked using a specific method.
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 172.18.139.130 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:dde:e538:2cd9:d9b1%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): {184.218.34.181, 101.17.187.43}
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 30:01:e2:f3:77:ff
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 bb:8b:6b:e7:b2:36
}
Resolving Issues with Wired and Wireless Connections
When it comes to the physical and data layer, individuals may utilize either a wired or wireless (Wi-Fi) medium to transmit data to their router.
Troubleshooting Solutions for Apple macOS / OSX
Regardless of the version of OSX/macOS being used, whether it’s 10.14.9, 11.2.8, or 12.2.6, there are a variety of tools available for troubleshooting. Unfortunately, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes invaluable, particularly for teams that embrace remote work and Work From Anywhere (WFA).
Utilizing In-Built Scripts for Assistance
A particularly useful tool on OSX/macOS is the sudo wdutil info, which provides a dump of the current wireless-related settings to the CLI, and can be configured to generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs, though much of it is only relevant to wireless at a specific point in time, 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 the user. For an interactive experience (despite minimal interaction), users may run sudo /usr/bin/sysdiagnose, which will prompt a privacy warning. When not run in the background, it should open Finder in the correct location, allowing users to navigate to /var/tmp or use Finder with Cmd+Shift+G to locate the path. It’s important to note that file sizes will be approximately 300MB more or less.
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