ipv4 vs ipv6

IPv4

Addresses are 32 bits (4 bytes) in length.
Address (A) resource records in DNS to map host names to IPv4 addresses.
Pointer (PTR) resource records in the IN-ADDR.ARPA DNS domain to map IPv4 addresses to host names
IPSec is optional and should be supported externally
Header does not identify packet flow for QoS handling by routers
Both routers and the sending host fragment packets.
Header includes a checksum.
Header includes options.
ARP uses broadcast ARP request to resolve IP to MAC/Hardware address.
Internet Group Management Protocol (IGMP) manages membership in local subnet groups.
Broadcast addresses are used to send traffic to all nodes on a subnet.
Configured either manually or through DHCP.
Must support a 576-byte packet size (possibly fragmented).

IPv6
Addresses are 128 bits (16 bytes) in length
Address (AAAA) resource records in DNS to map host names to IPv6 addresses.
Pointer (PTR) resource records in the IP6.ARPA DNS domain to map IPv6 addresses to host names.
IPSec support is not optional
Header contains Flow Label field, which Identifies packet flow for QoS handling by router.
Routers do not support packet fragmentation. Sending host fragments packets
Header does not include a checksum.
Optional data is supported as extension headers.
Multicast Neighbor Solicitation messages resolve IP addresses to MAC addresses.
Multicast Listener Discovery (MLD) messages manage membership in local subnet groups.
IPv6 uses a link-local scope all-nodes multicast address.
Does not require manual configuration or DHCP.
Must support a 1280-byte packet size (without fragmentation).