Extended Address SpaceThe address format is extended from 32 bits to 128 bits. This not only provides room for all anticipated needs, it allows for the use of ahierarchical address space structure to optimize global addressing.Stateless AutoconfigurationWhen a booting device comes up in IPv6 and asks for its network prefix, the device can get the prefix (or prefixes) from an IPv6 router onits link. It can then autoconfigure one or more global IPv6 addresses by using either the MAC address or a private random number to buildits unique IPv6 address.Stateless autoconfiguration uses three mechanisms for IPv6 address configuration:• Prefix Advertisement — Routers use “Router Advertisement” messages to announce the network prefix. Hosts then use theirinterface-identifier MAC address to generate their own valid IPv6 address.• Duplicate Address Detection (DAD) — Before configuring its IPv6 address, an IPv6 host node device checks whether that address isused anywhere on the network using this mechanism.• Prefix Renumbering — Useful in transparent renumbering of hosts in the network when an organization changes its service provider.NOTE: As an alternative to stateless autoconfiguration, network hosts can obtain their IPv6 addresses using the dynamic hostcontrol protocol (DHCP) servers via stateful auto-configuration.NOTE: Dell Networking OS provides the flexibility to add prefixes on Router Advertisements (RA) to advertise responses toRouter Solicitations (RS). By default, RA response messages are sent when an RS message is received.Dell Networking OS manipulation of IPv6 stateless autoconfiguration supports the router side only. Neighbor discovery (ND) messages areadvertised so the neighbor can use this information to auto-configure its address. However, received ND messages are not used to createan IPv6 address.NOTE: Inconsistencies in router advertisement values between routers are logged per RFC 4861. The values checked forconsistency include:• Cur Hop limit• M and O flags• Reachable time• Retrans timer• MTU options• Preferred and valid lifetime values for the same prefixOnly management ports support stateless auto-configuration as a host.The router redirect functionality in the neighbor discovery protocol (NDP) is similar to IPv4 router redirect messages. NDP uses ICMPv6redirect messages (Type 137) to inform nodes that a better router exists on the link.IPv6 HeadersThe IPv6 header has a fixed length of 40 bytes. This fixed length provides 16 bytes each for source and destination information and 8 bytesfor general header information.The IPv6 header includes the following fields:• Version (4 bits)• Traffic Class (8 bits)430 IPv6 Routing
