Dell C1048P Port Extender Networking Configuration Guide for the C9000 Series - Page 469

• Prefix Advertisement - Routers use "Router Advertisement" messages to announce the network prefix. Hosts then use their interface-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 is used 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 host control protocol (DHCP) servers via stateful auto-configuration. NOTE: The system provides the flexibility to add prefixes on Router Advertisements (RA) to advertise responses to Router Solicitations (RS). By default, RA response messages are sent when an RS message is received. The manipulation of IPv6 stateless autoconfiguration supports the router side only. Neighbor discovery (ND) messages are advertised so the neighbor can use this information to auto-configure its address. However, received ND messages are not used to create an IPv6 address. NOTE: Inconsistencies in router advertisement values between routers are logged per RFC 4861. The values checked for consistency include: • Cur Hop limit • M and O flags • Reachable time • Retrans timer • MTU options • Preferred and valid lifetime values for the same prefix Only 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 ICMPv6 redirect messages (Type 137) to inform nodes that a better router exists on the link. IPv6 Headers The IPv6 header has a fixed length of 40 bytes. This fixed length provides 16 bytes each for source and destination information and 8 bytes for general header information. The IPv6 header includes the following fields: • Version (4 bits) • Traffic Class (8 bits) • Flow Label (20 bits) • Payload Length (16 bits) • Next Header (8 bits) • Hop Limit (8 bits) • Source Address (128 bits) • Destination Address (128 bits) IPv6 provides for extension headers. Extension headers are used only if necessary. There can be no extension headers, one extension header or more than one extension header in an IPv6 packet. Extension headers are defined in the Next Header field of the preceding IPv6 header. IPv6 Routing 469