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Understanding the Functioning of Internet Addressing
When utilizing the Internet, individuals may have a Public IPv4 address such as 122.61.61.214 or an IPv6 address like 2000:2c7c:c1a0:53a3:3c4e:cefd:6d46:4984. These addresses can be verified at https://test-ipv6.com/. Nevertheless, conveying these addresses to those who are not technologically inclined, or even referencing MAC addresses such as e0:c1:91:85:4f:d4, can lead to errors and can become intricate. Additionally, this method does not provide historical data, particularly when past issues arose.
Navigating the Internet
In order to access a website like https://greenfelder.org, individuals initially connect to a DNS server to convert the host portion (greenfelder) combined with the Top Level Domain (org) of the URL into an IP address such as 184.34.8.207. The computer and browser also transmits its type with all web requests, 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
Understanding the Significance of Default Gateways
The default gateway is typically an automatically configured address via DHCP. Users receive a default gateway like 192.168.32.181 (commonly ending in .1 or .254 depending on the scope size) and this is where the computer directs all its traffic to be routed onwards. For IPv6, a comprehensive examination is available in how-to-fix-ipv6-connectivity/ but it can be checked on Mac or Linux using 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 192.168.32.181 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:d010:ad7f:19c:a252%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): {91.142.193.87, 33.142.202.150}
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 e0:c1:91:85:4f:d4
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 45:98:57:bc:6e:b2
}
Resolving Connectivity Issues in Wired and Wireless Networks
When it comes to transmitting data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX Users
Regardless of whether you are using macOS or OSX version 10.13.5, 11.5.4, or 12.3.7, there are various troubleshooting tools available. However, these tools do not provide a series of correlated values over time, making automated remote troubleshooting more beneficial, especially for teams working remotely or following a Work From Anywhere (WFA) approach.
Utilizing Built-in Scripts for Assistance
One useful tool for OSX/macOS users is the sudo wdutil info command, which provides current wireless settings and can also be configured to generate specific troubleshooting logs. Additionally, the sysdiagnose tool can generate a wide range of logs, although many are only relevant to a particular point in time, similar to wdutil.
To run sysdiagnose in the background and generate logs at /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. For an interactive experience, run sudo /usr/bin/sysdiagnose and heed the privacy warning. The file sizes generated are approximately 300MB, so be mindful of storage space.
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