How Can I Understand OSX Internet Connection
Understanding Internet Addressing
When connecting to the Internet, you are assigned either a Public IPv4 address such as 217.254.159.244 or an IPv6 address like 2000:3722:798b:5a14:b73c:1127:b4c3:d31. This can be verified using https://test-ipv6.com/. However, explaining or dealing with these addresses, as well as MAC addresses like 33:76:bc:7a:59:fd, can be prone to errors and become complex for non-technical individuals. Additionally, no historical data is provided, particularly when troubleshooting past issues.
Navigating Web Access
When attempting to reach a website like https://watsica.biz, the first step involves accessing a DNS server to convert the host portion (watsica) combined with the Top Level Domain (biz) of the URL into an IP address, such as 23.228.69.144. Your computer and browser include its type in all web requests, for example:
Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
Significance of Default Gateways
The default gateway is typically an automatically obtained address through DHCP. It is usually assigned as a default gateway address, such as 192.0.0.13 (often ending in .1 or .254 based on the scope size), and serves as the point where your computer directs all its traffic to be routed further. For IPv6, detailed instructions are available at how-to-fix-ipv6-connectivity/, but you can also verify 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 192.0.0.13 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:c08a:756e:82a7:d562%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): {136.240.182.106, 17.77.142.43}
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 33:76:bc:7a:59:fd
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 79:65:52:5d:03:06
}
Resolving Issues with Wired and Wireless Connections
When it comes to sending data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Solutions for Apple macOS / OSX
Regardless of whether you are using OSX/macOS version 10.12.4, 11.4.3, or 12.1.2, there are several troubleshooting tools available. However, these tools do not provide a series of correlated values over time, which is where automated remote troubleshooting becomes beneficial, especially for remote work and Work From Anywhere (WFA) teams.
Effective Built-in Scripts
An essential tool for troubleshooting on OSX/macOS is sudo wdutil info, which provides a CLI dump of current wireless settings and generates specific logs for troubleshooting. Moreover, the sysdiagnose tool can be used to generate a variety of logs, although much of it is only relevant to wireless settings, similar to wdutil.
To run sysdiagnose in the background and generate logs in /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. For interactive use, run sudo /usr/bin/sysdiagnose and be mindful of the large file sizes of about 300MB.
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