How Do You Understand OSX Internet Connection
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 145.100.115.129, or an IPv6 address, such as 2000:9b60:2b0a:6228:41ba:8fa4:db2e:2fee. This information can be verified at https://test-ipv6.com/. However, trying to communicate and remember these addresses, as well as MAC addresses like 45:a1:60:d6:10:bf, can be error-prone and complex, especially for those who are not tech-savvy. This also lacks historical data, which is crucial for troubleshooting past issues.
Navigating the World Wide Web
In order to access a website like https://kunde.org, you first reach out to a DNS server to translate the host name (kunde) and the Top Level Domain (org) of the URL into an IP address, such as 54.2.162.163. When making web requests, your computer and browser also transmit information about its type, for example: Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
The Significance of Default Gateways
Your default gateway is usually assigned automatically through DHCP and is represented by an address like 172.21.85.22 (typically ending in .1 or .254 depending on the scope size). This is where your computer sends all its traffic to be routed further. For IPv6, you can find more detailed information in our article how-to-fix-ipv6-connectivity/, or you can perform the check on Mac or Linux with the following command:
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 172.21.85.22 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 fe80:9eea:4998:4033:ca00%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): {137.213.57.87, 105.87.219.217}
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 45:a1:60:d6:10:bf
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 73:70:9a:2f:57:e4
}
Solutions for Resolving Connectivity Issues
When it comes to transferring data to your router, you might be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Steps to Take on Apple’s macOS / OSX
No matter which version of OSX/macOS you have, whether it’s 10.12.4, 11.0.3, or 12.3.6, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes essential, particularly for teams that support remote work and Work From Anywhere (WFA).
Pre-Installed Scripts That Offer Assistance
A highly 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 troubleshooting logs. Additionally, the sysdiagnose tool can be used to produce a wide range of logs, although much of it is point-in-time data in relation to wireless, similar to wdutil.
By running sudo nohup /usr/bin/sysdiagnose -u &, the tool will run in the background and write logs to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively (although there is not much interaction), you can execute sudo /usr/bin/sysdiagnose and it will display 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 or use Cmd+Shift+G to point Finder to the path. Be aware that the file sizes are approximately 300MB.
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