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Explanation of Internet Addressing
When connecting to the Internet, you will receive either a Public IPv4 address, such as 130.14.212.185, or an IPv6 address, like 2000:1122:fffb:ab92:cf0d:3b09:765c:2040. The verification of these addresses can be done at https://test-ipv6.com/. However, for those who are not technologically inclined, transmitting these addresses, or even citing MAC addresses such as ba:26:76:e2:e6:f2, can be prone to errors and quickly become complicated. Additionally, this method does not provide any historical data, especially when it comes to past issues.
Process of Accessing the Internet
In order to access a webpage like https://langworth.net, the first step is to access a DNS server to convert the host part (langworth) combined with the Top Level Domain (net) of the URL into an IP address, such as 11.218.59.202. Whenever you make a web request, your computer and browser actually sends its type along with it, for example:
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A
Significance of Default Gateways
Typically, your default gateway is an address that is automatically configured via DHCP. This default gateway, such as 10.63.132.144 (frequently ending in .1 or .254, based on the scope size), is the point where your computer sends all of its traffic to be routed further. To learn more about setting up IPv6, you can refer to how-to-fix-ipv6-connectivity/ or you can verify the settings on a Mac or Linux using the following command:
route -n
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 10.63.132.144 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 fe80:93de:c750:350a:1904%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): {211.155.52.30, 207.53.1.98}
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 ba:26:76:e2:e6:f2
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 33:ee:3e:41:6f:0d
}
Resolve Connectivity Issues with Wired and Wireless Networks
When it comes to transmitting data to your router, you might be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX Users
Regardless of the version of OSX/macOS you are using, whether it’s 10.14.5, 11.1.6, or 12.3.6, there are various methods for troubleshooting connectivity issues. However, the manual actions and scripts available do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes essential, particularly for teams that have embraced remote work and Work From Anywhere (WFA).
Useful Built-in Tools for Troubleshooting
One valuable tool on OSX/macOS is sudo wdutil info, which generates a dump of the current wireless settings to the CLI and can be configured to produce specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, though much of it is only relevant to wireless settings, 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. To run it interactively, you can execute sudo /usr/bin/sysdiagnose and 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 using Finder with Cmd+Shift+G. Note that the file sizes are approximately 300MB.
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