The main feature of IPv6 that is driving adoption today is the larger address space: addresses in IPv6 are 128 bits long versus 32 bits in IPv4.
The larger address space avoids the potential exhaustion of the IPv4 address space without the need for [[network address translation]] (NAT) and other devices that break the [[end-to-end]] nature of Internet traffic. NAT may still be necessary in rare cases, but Internet engineers recognize that it will be difficult in IPv6 and are trying to avoid it whenever possible. It also makes administration of medium and large networks simpler, by avoiding the need for complex [[subnetting]] schemes. Subnetting will, ideally, revert to its purpose of logical segmentation of an [[IP network]] for optimal [[routing]] and access.
The drawback of the large address size is that IPv6 carries some bandwidth overhead over IPv4, which may hurt regions where bandwidth is limited ([[ROHC|header compression]] can sometimes be used to alleviate this problem). This also makes human memorization of IPv6 addresses much harder compared to IPv4 addresses, often impossible due to their length; use of the [[Domain Name System]] (DNS) is necessary.
