IPv6 features
Simplified header format
IPv6 removes several IPv4 header fields or moves them to the IPv6 extension headers to reduce the length of the basic IPv6 packet header. The basic IPv6 packet header has a fixed length of 40 bytes to simplify IPv6 packet handling and improve forwarding efficiency. Although the IPv6 address size is four times the IPv4 address size, the basic IPv6 packet header size is only twice the size of the option-less IPv4 packet header.
Figure 58: IPv4 packet header format and basic IPv6 packet header format
Larger address space
IPv6 can provide 3.4 x 1038 addresses to meet the requirements of hierarchical address assignment for both public and private networks.
Hierarchical address structure
IPv6 uses a hierarchical address structure to speed up route lookup and reduce the IPv6 routing table size through route aggregation.
Address autoconfiguration
To simplify host configuration, IPv6 supports stateful and stateless address autoconfiguration.
Stateful address autoconfiguration enables a host to acquire an IPv6 address and other configuration information from a server (for example, a DHCPv6 server). For more information about DHCPv6 server, see "Configuring the DHCPv6 server."
Stateless address autoconfiguration enables a host to automatically generate an IPv6 address and other configuration information by using its link-layer address and the prefix information advertised by a router.
To communicate with other hosts on the same link, a host automatically generates a link-local address based on its link-layer address and the link-local address prefix (FE80::/10).
Built-in security
IPv6 defines extension headers to support IPsec. IPsec provides end-to-end security and enhances interoperability among different IPv6 applications.
QoS support
The Flow Label field in the IPv6 header allows the device to label the packets of a specific flow for special handling.
Enhanced neighbor discovery mechanism
The IPv6 neighbor discovery protocol uses a group of ICMPv6 messages to manage information exchange among neighboring nodes on the same link. The group of ICMPv6 messages replaces ARP messages, ICMPv4 router discovery messages, and ICMPv4 redirect messages and provides a series of other functions.
Flexible extension headers
IPv6 eliminates the Options field in the header and introduces optional extension headers to provide scalability and improve efficiency. The Options field in the IPv4 packet header contains a maximum of 40 bytes, whereas the IPv6 extension headers are restricted to the maximum size of IPv6 packets.