ppatux

Simple IPv6 detector widget for WordPress to show if user is connecting with IPv6 or IPv4.
Additionaly, it makes a link to a whois service with the ip address.
It was born because of my own blog. I needed to include a little box that shows users ip and different messages depending on the ip version.
The idea behind this is to promote and leave a way to discover and make sense about the ipv4 address space limits.

IPv6 Detector

Simple IPv6 detector widget for WordPress to show if user is connecting with IPv6 or IPv4.

Cris van Geel

This plugin provides detailed info about an IPv4 or IPv6 subnet.
How do you use it? Place the IP adres and CIDR subnet between [subnetinfo] and [/subnetinfo] brackets.
Use the following format : [subnetinfo]FE80:0000:0000:0000:0202:B3FF:FE1E:8329/64[/subnetinfo]
or [subnetinfo]192.168.100.10/24[/subnetinfo]
It will be automatically parsed to a nice layout.
The address identification and all calculation are carried out within the plugin itself.
A link to IANA is created in the results to the corresponding RFC which describes more details about the specific IP range. 
For some special IP ranges that are not directly described in an RFC, a link to a relevant website or Wikipedia site is offered.
<h3>Arbitrary section</h3>

subnetinfo

Provides detailed information about the IP adress and subnet using a shortcode.

IPv6 Detector vs subnetinfo