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The Fundamentals of Internet Addressing
Internet addressing involves obtaining a unique IPv4 address like 64.232.253.219 or an IPv6 address like 2000:4596:d1a2:fc92:ef1:f39a:2130:3114. You can verify this at https://test-ipv6.com/. However, conveying these addresses, or even referring to MAC addresses like 01:2e:28:78:1f:e9, can be prone to errors and becomes complex. Moreover, this does not provide historical data, particularly related to past issues.
Navigating Through the Internet
When accessing a website such as https://damore.info, the first step is to access a DNS server to convert the host portion (damore) combined with the Top Level Domain (info) of the URL to an IP address like 224.250.31.112. Your computer and browser include its type in all web requests e.g. Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
Understanding the Significance of Default Gateways
The default gateway is usually an automatically configured address through DHCP. You receive a default gateway like 10.24.151.33 (although they typically end in .1 or .254 based on the scope size) and this is where your computer directs all its traffic to be routed. For IPv6 connectivity, comprehensive guidance is available at how-to-fix-ipv6-connectivity/ but you can verify on Mac or Linux using:
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 10.24.151.33 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 f8:a52e:e1e4:7e80:27c2:798c:d48e:f0c7%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): {194.4.246.112, 219.32.154.232}
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 01:2e:28:78:1f:e9
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 89:ff:29:9a:35:c2
}
Resolving Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
No matter which version of OSX/macOS you’re running - whether it’s 10.14.6, 11.2.1, or 12.1.6 - 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 valuable, especially for teams embracing remote work and Work From Anywhere (WFA).
Utilizing In-Built Scripts for Assistance
One useful tool on OSX/macOS is the sudo wdutil info, which dumps current wireless-related settings to the CLI and can 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 point-in-time only in relation to wireless, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz. For an interactive run (though there’s not much interaction), you can use 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 or use Cmd+Shift+G in Finder to point it to the path. Just be aware of the file size, which is about 300MB.
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