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Understanding the Basics of Internet Addressing
When using the Internet, individuals may be assigned a Public IPv4 address such as 156.121.34.107 or an IPv6 address like 2000:70cf:78de:2077:9089:d13c:f971:52d2. A helpful tool for checking your address is available at https://test-ipv6.com/. However, attempting to convey these addresses to those who are not technically inclined, or even articulating MAC addresses like de:d6:75:f6:98:d5, can lead to errors and complexity. Furthermore, this method does not provide historical data, particularly from past issues.
Navigating Websites
When attempting to access a web page such as https://wolf.name, the first step involves connecting to a DNS server to convert the host portion (wolf) in combination with the Top Level Domain (name) of the URL into an IP address, for example, 69.234.167.180. It is important to note that the web requests sent by your computer and browser typically contain the specification of their type, such as:
Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)
Recognizing the Significance of Default Gateways
Typically, your default gateway consists of an address that is automatically configured through DHCP, resulting in a default gateway like 172.20.82.97 (typically ending in .1 or .254 based on the scope size). This serves as the point to which your computer directs all of its traffic to be further routed. For IPv6 inquiries, comprehensive information can be found at how-to-fix-ipv6-connectivity/ or through a check on Mac or Linux with the command:
/command-here
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 172.20.82.97 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:cb41:318b:a1f8:af7f%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): {222.2.86.173, 88.201.88.183}
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 de:d6:75:f6:98:d5
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 01:e3:76:c8:8a:88
}
Resolving Issues with Wired or Wireless Connectivity
When it comes to sending data to your router, you might be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of whether you are using OSX/macOS versions like 10.14.1, 11.6.6, or 12.2.2, there are various tools available for addressing connectivity issues. 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 are embracing remote work and Work From Anywhere (WFA).
Embedded Scripts for Assistance
An extremely useful tool on OSX/macOS is sudo wdutil info, which dumps current wireless settings to the CLI and can also be configured to generate specific troubleshooting logs. Moreover, the sysdiagnose tool can be used to produce a wide array of logs, although much of it is only relevant to wireless connectivity just like wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will generate logs in /var/tmp/<blah>.tar.gz for you. Alternatively, if you prefer to run it interactively (even though there is not much interaction), you can execute sudo /usr/bin/sysdiagnose, which will prompt 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 mindful of the file sizes, which are approximately 300MB or slightly more.
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