How Can I Understand MacOS Internet
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 0.105.146.51, or an IPv6 address, like 2000:9e03:ce0e:fbd3:3a21:e0be:8b8d:cb00. https://test-ipv6.com/ can help you verify your address. However, explaining and sharing these addresses, as well as MAC addresses like 26:e8:f4:7a:6f:98, can be prone to errors and quickly become complicated, especially for those who are not technically inclined. Furthermore, this method does not provide historical data, particularly during previous issues.
Navigating the World Wide Web
In order to access a website such as https://luettgen.name, you first need to contact a DNS server to convert the host part (luettgen) together with the Top Level Domain (name) of the URL into an IP address, like 33.24.250.57. Your computer and browser send their type along with every web request, for example: Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)
The Significance of Default Gateways
Your default gateway is typically an automatically configured address through DHCP. It usually ends in .1 or .254, depending on the scope size, such as 192.168.165.175, and is where your computer forwards all of its traffic for routing. For IPv6, detailed instructions can be found in our blog post how-to-fix-ipv6-connectivity/, but on Mac or Linux, you can verify this by:
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 192.168.165.175 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 fe80:82a7:883a:eac8:e603%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): {240.114.203.248, 86.249.235.212}
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 26:e8:f4:7a:6f:98
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 3b:f2:25:c6:2b:40
}
Troubleshooting Issues with Wired and Wireless Connections
When it comes to sending data to your router, you may be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Tips for Managing Issues on Apple macOS / OSX
No matter which version of OSX/macOS you’re running - whether it’s 10.15.1, 11.3.5, or 12.3.7 - there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes essential, especially for teams embracing remote work and Work From Anywhere (WFA).
Useful Built-in Tools
One incredibly useful tool on OSX/macOS is 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. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant to wireless settings, similar to wdutil.
To run it in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, use the command sudo /usr/bin/sysdiagnose, which 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 using Finder with Cmd+Shift+G. However, be aware of the file sizes, which can be around 300MB.
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P.S. Tips For Remote Network and Client Support
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