Comparison of IPv4 and IPv6

Table 1-1 highlights some of the key differences between IPv4 and IPv6.

Table 1-1. Differences Between IPv4 and IPv6

IPv4	IPv6
Source and destination addresses are 32 bits (4 bytes) in length.	Source and destination addresses are 128 bits (16 bytes) in length. For more information, see Chapter 3, "IPv6 Addressing."
IPSec support is optional.	IPSec support is required. For more information, see Chapter 4, "The IPv6 Header."
No identification of packet flow for QoS handling by routers is present within the IPv4 header.	Packet flow identification for QoS handling by routers is present within the IPv6 header using the Flow Label field. For more information, see Chapter 4, "The IPv6 Header."
Fragmentation is performed by the sending host and at routers, slowing router performance.	Fragmentation is performed only by the sending host. For more information, see Chapter 4, "The IPv6 Header."
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 must be able to reassemble a 1,500-byte packet. For more information, see Chapter 4, "The IPv6 Header."
Header includes a checksum.	Header does not include a checksum. For more information, see Chapter 4, "The IPv6 Header."
Header includes options.	All optional data is moved to IPv6 extension headers. For more information, see Chapter 4, "The IPv6 Header."
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. For more information, see Chapter 6, "Neighbor Discovery."
Internet Group Management Protocol (IGMP) is used to manage local subnet group membership.	IGMP is replaced with Multicast Listener Discovery (MLD) messages. For more information, see Chapter 7, "Multicast Listener Discovery."
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 is required. For more information, see Chapter 6, "Neighbor Discovery."
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. For more information, see "Multicast IPv6 Addresses" in Chapter 3, "IPv6 Addressing."
Must be configured either manually or through DHCP for IPv4.	Does not require manual configuration or DHCP for IPv6. For more information, see Chapter 8, "Address Autoconfiguration."
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. For more information, see Chapter 9, "IPv6 and Name Resolution."
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 domains to map IPv6 addresses to host names. For more information, see Chapter 9, "IPv6 and Name Resolution."