| IPV4 | IPV6 |
|---|---|
| Source and destination addresses are 32 bits (4 bytes) in length. | Source and destination addresses are 128 bits (16 bytes) in length. |
| IPSec support is optional.IPSec support is required. | |
| IPv4 header does not identify packet flow for QoS handling by routers.IPv6 header contains Flow Label field, which identifies packet flow for QoS handling by router. | |
| Both routers and the sending host fragment packets.Only the sending host fragments packets; routers do not. | |
| Header includes a checksum. Header does not include a checksum. | |
| Header includes optionsAll optional data is moved to IPv6 extension headers. | |
| Address Resolution Protocol (ARP) uses broadcast ARP Request frames to resolve an IP address to a link-layer address. Multicast Neighbor Solicitation messages resolve IP addresses to link-layer addresses. | |
| Internet Group Management Protocol (IGMP) manages membership in local subnet groups.Multicast Listener Discovery (MLD) messages manage membership in local subnet groups. | |
| ICMP Router Discovery is used to determine the IPv4 address of the best default gateway, and it is optional.ICMPv6 Router Solicitation and Router Advertisement messages are used to determine the IP address of the best default gateway, and they are required. | |
| Broadcast addresses are used to send traffic to all nodes on a subnet.IPv6 uses a link-local scope all-nodes multicast address. | |
| Must be configured either manually or through DHCP. Does not require manual configuration or DHCP. | |
| Uses host address (A) resource records in Domain Name System (DNS) to map host names to IPv4 addresses. Uses host address (AAAA) resource records in DNS to map host names to IPv6 addresses. | |
| Uses pointer (PTR) resource records in the IN-ADDR.ARPA DNS domain to map IPv4 addresses to host names.Uses pointer (PTR) resource records in the IP6.ARPA DNS domain to map IPv6 addresses to host names. | |
| Must support a 576-byte packet size (possibly fragmented).Must support a 1280-byte packet size (without fragmentation). |