IPv6 features
Header format simplification
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 to improve forwarding efficiency. Although IPv6 address size is four times larger than IPv4 address size, the basic IPv6 packet header size is only twice the size of the option-less IPv4 packet header.
Figure 52: IPv4 packet header format and basic IPv6 packet header format
Larger address space
The source and destination IPv6 addresses are 128 bits (or 16 bytes) long. IPv6 can provide 3.4 x 1038 addresses to meet the requirements of hierarchical address division and the allocation of public and private addresses.
Hierarchical address structure
IPv6 uses hierarchical address structure to speed up route lookups 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 DHCP 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 for network security solutions and enhances interoperability among different IPv6 applications.
QoS support
The Flow Label field in the IPv6 header allows the device to label the packets and facilitates the special handling of a flow.
Enhanced neighbor discovery mechanism
The IPv6 neighbor discovery protocol is implemented through a group of Internet Control Message Protocol version 6 (ICMPv6) messages to manage the information exchange among neighboring nodes on the same link. The group of ICMPv6 messages replaces Address Resolution Protocol (ARP) messages, Internet Control Message Protocol version 4 (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 only.