Describe and compare IPv4 and IPv6 addressing schemes.

IPv4
IPv4 stands for Internet Protocol version 4. It is the underlying technology that makes it possible for us to connect our devices to the web. Whenever a device access the Internet (whether it's a PC, Mac, smartphone or other device), it is assigned a unique, numerical IP address such as 99.48.227.227. To send data from one computer to another through the web, a data packet must be transferred across the network containing the IP addresses of both devices.

IPv4 uses 32-bit addresses for Ethernet communication in five classes, named A, B, C, D and E. Classes A, B and C have a different bit length for addressing the network host. Class D addresses are reserved for multicasting, while class E addresses are reserved for future use.

Class A has subnet mask 255.0.0.0 or /8, B has subnet mask 255.255.0.0 or /16 and class C has subnet mask 255.255.255.0 or /24. For example, with a /16 subnet mask, the network 192.168.0.0 may use the address range of 192.168.0.0 to 192.168.255.255. Network hosts can take any address from this range; however, address 192.168.255.255 is reserved for broadcast within the network.

IPv6
IPv6 is the next generation protocol for Internet networking. IPv6 expands on the current Internet Protocol standard known as IPv4. Compared to IPv4, IPv6 offers better addressing, security and other features to support large worldwide networks. 
In IPv6, IP addresses change from the current 32-bit standard and dotted decimal notation to a new 128-bit address system. IPv6 addresses remain backward compatible with IPv4 addresses. For example, the IPv4 address "192.168.100.32" may appear in IPv6 notation as "0000:0000:0000:0000:0000:0000:C0A8:6420" or "::C0A8:6420". 

Main reasons for running out of IPv4.
The IPv4 protocol was created in 1981 like a technology supposed to last for a very long time, with an addressing space of 4000 million of addresses, but the enormous growth of the internet and the way the addresses were assigned (classes A, B and C), resulted in a serious lack of addresses. There are several methods that avoid the total run out of addresses: PPP/DHCP (address sharing), CIDR (classless inter-domain routing) and NAT (network address translation), but do not seem to be enough in a few years, specially having into account the growing number of devices that need a permanent allocation of an IP address (UMTS, DSL, etc), and the applications that are end-to-end, and are not compatible with NAT (IPsec, VoIP, etc.).

Another problem is that, because of being designed many years ago, the functionalities involved with security, mobility and quality are handled by additional protocols, because they are not integrated in the protocol itself.

So, these 2 problems, plus the fact of the great growth of the number of elements in the routing tables motivated the necessity of a new version of the protocol became very important, so a new working group of the Internet Engineering Task Force (IETF) was created with the name: “IP next generation” (IPng). And some time later, the name was changed to IPv6. The main characteristics of this protocol had to be the following:

·         Larger addressing space, structured addresses and no addresses classes.

·         Automatic configuration.

·         Simplified routing.

·         Better structuring options for the networks.

·         Improved security features.

·         Support for real-time and multimedia services.

IPv4/IPv6 Differences

Here are some of the major differences between IPv4 and IPv6. Both standards are extensive and many features are less obvious and important for only some environments.

 

	IPv4	IPv6
Address	32 bits (4 bytes) 12:34:56:78	128 bits (16 bytes) 1234:5678:9abc:def0: 1234:5678:9abc:def0
Packet size	576 bytes required, fragmentation optional	1280 bytes required without fragmentation
Packet fragmentation	Routers and sending hosts	Sending hosts only
Packet header	Does not identify packet flow for QoS (Quality of service)  handling	Contains Flow Label field that specifies packet flow for QoS handling
	Includes a checksum	Does not include a checksum
	Includes options up to 40 bytes	Extension headers used for optional data
DNS records	Address (A) records, maps host names	Address (AAAA) records, maps host names
	Pointer (PTR) records, IN-ADDR.ARPA DNS domain	Pointer (PTR) records, IP6.ARPA DNS domain
Address configuration	Manual or via DHCP	Stateless address autoconfiguration (SLAAC) using Internet Control Message Protocol version 6 (ICMPv6) or DHCPv6
IP to MAC resolution	broadcast ARP	Multicast Neighbor Solicitation
Local subnet group management	Internet Group Management Protocol (IGMP)	Multicast Listener Discovery (MLD)
Broadcast	Yes	No
Multicast	Yes	Yes
IPSec	optional, external	required