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.

No identification of packet flow for quality of service (QoS) handling by routers is present within the IPv4 header.

Packet flow identification for QoS handling by routers is included in IPv6 header using the Flow Label field.

Fragmentation is done by both routers and the sending host.

Fragmentation is not done by routers, only by the sending host.

Header includes a checksum.

Header does not include a checksum.

Header includes options.

All optional data is moved to IPv6 extension headers.

Address Resolution Protocol (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 memberships.

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.

ICMP Router Discovery is replaced with ICMPv6 Router Solicitation and Router Advertisement messages and is required.

Broadcast addresses are used to send traffic to all nodes on a subnet.

There are no IPv6 broadcast addresses. Instead, a link-local scope-all-nodes multicast address is used.

Must be configured either manually or through DHCP.

Does not require manual configuration or DHCP.

Uses host address (A) resource records in the Domain Name System (DNS) to map host names to IPv4 addresses.

Uses host address (AAAA) resource records in the Domain Name System (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.INT 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).