How Can I Understand Mac Internet Connection
Understanding Internet Addressing
When using the Internet, you are assigned a unique address, such as 148.119.177.167 for IPv4 or 2000:ec9d:f468:1c56:ffaa:9fb1:1f03:3d15 for IPv6. The process of communicating and identifying these addresses, as well as MAC addresses like cb:a0:e5:ba:18:09, can be complicated and error-prone, especially for non-technical users. There is also a lack of historical data available, which is important when dealing with past issues.
The Process of Accessing Websites
When accessing a website, such as https://sipes-homenick.info, you first need to contact a DNS server to translate the hostname (sipes-homenick) and the Top Level Domain (info) into an IP address, such as 131.200.102.55. Your computer and browser also communicate their type with every web request, for example: Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
The Significance of Default Gateways
The default gateway, typically assigned automatically through DHCP, serves as the central routing point for all the traffic from your computer. For IPv6, more detailed information is available at how-to-fix-ipv6-connectivity/, and users of Mac or Linux systems can check this configuration 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 192.0.0.144 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:fb09:5ebf:262:431d%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): {25.123.2.10, 197.12.156.156}
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 cb:a0:e5:ba:18:09
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 e4:75:7f:a8:eb:a0
}
Resolving Connectivity Issues for Wired and Wireless Networks
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 Methods for Apple macOS / OSX
Regardless of the version of OSX/macOS you are running, whether it’s 10.13.6, 11.1.5, or 12.2.5, there is a variety of troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time. Automated remote troubleshooting becomes essential, especially for teams that embrace remote work and Work From Anywhere (WFA).
Useful Embedded Scripts
An example of a valuable tool on OSX/macOS is sudo wdutil info, which provides a CLI dump of current wireless settings and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a comprehensive range of logs, although much of it is only point-in-time in relation to wireless, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz. Alternatively, you can run sudo /usr/bin/sysdiagnose interactively, though it will give a privacy warning. When not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp manually or by using Cmd+Shift+G in Finder to point to the path. Keep in mind that the file sizes are approximately 300MB or less.
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