Internet Protocol Version 4 is the 4rth revision of Internet protocol, its generally a 32-bit address consisting of 4 numbers separated by periods for example 12.342.7.89
Internet Protocol Version 6 is the 6th revision and intended to replace IPv4, it is a 128 bit address written in hexadecimal and separated by colons for example 8ffe:1900:4545:7:336:f3ff:fe19:34c
Since there a limited number of potential IPv4 address (around 4 billion) we are rapidly running out of unused Ipv4 addresses to assign to new devices this is called IPv4 exhaustion. However since this is the older and dominant form most computers still have one, your ISP however is anticipating the move into IPv6 and has therefore assigned you an address
IPv6 also provides a number of other benefits included but not limited to
- No more NAT (Network Address Translation)
- Auto-configuration
- No more private address collisions
- Better multicast routing
- Simpler header format
- Simplified, more efficient routing
- True quality of service (QoS), also called "flow labeling"
- Built-in authentication and privacy support
- Flexible options and extensions
- Easier administration (no more DHCP)
Most modern servers will typically try to connect to your IPv6 address first and then your IPv4, many modern OS's functions may rely entirely on IPv6 therefore it is not recommended for you to disable your IPv6 although this will force your computer to connect through IPv4.
The security vulnerabilities with IPv6 are almost entirely related to VPN's as they sometimes bypass IPv6 entirely, however this is no longer becoming an issue and most new VPN providers are switching to provide IPV6 compatibility.
There is hardware that exists that does not support IPv6. Your ISP is not aware of what hardware you have. They own the addresses so it costs them nothing to assign you both. – Ramhound – 2016-02-09T00:39:50.740
6You can expect a less reliable connection if you disable IPv6. A lot of the providers who are enabling IPv6 are doing so because they have run out of IPv4 addresses, and your IPv4 connection might go through a CGN. Besides modern browsers can fail over between IPv4 and IPv6 in less than a second, so having both enabled can provide additional resilience to some network failures. – kasperd – 2016-02-09T09:18:29.993