IPv4 | IPv6 |
| Source and destination addresses are 32 bits (4 ytes) in length. | Source and destination addresses are 128 bits (16 bytes) in length. |
| IPsec header support is optional. | IPsec header support is required. |
| No identification of packet flow for prioritized delivery handling by routers is present within the IPv4 header. | Packet
flow identification for prioritized delivery handling by routers is
present within the IPv6 header using the Flow Label field. |
| Fragmentation is performed by the sending host and at routers, slowing router performance. | Fragmentation is performed only by the sending host. |
| Has no link-layer packet-size requirements and must be able to reassemble a 576-byte packet. | Link layer must support a 1,280-byte packet and be able to reassemble a 1,500-byte packet. |
| Header includes a checksum. | Header does not include a checksum. |
| Header includes options. | All optional data is moved to IPv6 extension headers. |
| ARP uses broadcast ARP Request frames to resolve an IPv4 address to a link-layer address. | ARP Request frames are replaced with multicast Neighbor Solicitation messages. |
| Internet Group Management Protocol (IGMP) is used to manage local subnet group membership. | IGMP is replaced with Multicast Listener Discovery (MLD) messages. |
| ICMP Router Discovery is used to determine the IPv4 address of the best default gateway and is optional. | ICMPv4 Router Discovery is replaced with ICMPv6 Router Solicitation and Router Advertisement messages, and it is required. |
| Broadcast addresses are used to send traffic to all nodes on a subnet. | There are no IPv6 broadcast addresses. Instead, a linklocal scope all-nodes multicast address is used. |
| Must be configured either manually or through DHCP for IPv4. | Does not require manual configuration or DHCP for IPv6. |
| Uses host address (A) resource records in the Domain Name System (DNS) to map host names to IPv4 addresses. | Uses AAAA records in the 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. |