Configuring IPv6 for Gigabit Ethernet Interfaces
S e n d d o c u m e n t a t i o n c o m m e n t s t o m d s f e e d b a c k - d o c @ c i s c o . c o m
acknowledgment that the forward path is still working (neighbor advertisement messages that have the
solicited flag set to a value of 1 are sent only in response to a neighbor solicitation message). Unsolicited
messages confirm only the one-way path from the source to the destination node; solicited neighbor
advertisement messages indicate that a path is working in both directions.
A neighbor advertisement message that has the solicited flag set to a value of 0 must not be considered
as a positive acknowledgment that the forward path is still working.
Neighbor solicitation messages are also used in the stateless autoconfiguration process to verify the
uniqueness of unicast IPv6 addresses before the addresses are assigned to an interface. Duplicate address
detection is performed first on a new, link-local IPv6 address before the address is assigned to an
interface (the new address remains in a tentative state while duplicate address detection is performed).
Specifically, a node sends a neighbor solicitation message with an unspecified source address and a
tentative link-local address in the body of the message. If another node is already using that address, the
node returns a neighbor advertisement message that contains the tentative link-local address. If another
node is simultaneously verifying the uniqueness of the same address, that node also returns a neighbor
solicitation message. If no neighbor advertisement messages are received in response to the neighbor
solicitation message and no neighbor solicitation messages are received from other nodes that are
attempting to verify the same tentative address, the node that sent the original neighbor solicitation
message considers the tentative link-local address to be unique and assigns the address to the interface.
Every IPv6 unicast address (global or link-local) must be checked for uniqueness on the link; however,
until the uniqueness of the link-local address is verified, duplicate address detection is not performed on
any other IPv6 addresses associated with the link-local address.
Router discovery performs both router solicitation and router advertisement. Router solicitations are sent
by hosts to all-routers multicast addresses. Router advertisements are sent by routers in response to
solicitations or unsolicited and contain default router information as well as additional parameters such
as the MTU and hop limit.
IPv6 Stateless Autoconfiguration
All interfaces on IPv6 nodes must have a link-local address, which is automatically configured from the
identifier for an interface and the link-local prefix FE80::/10. A link-local address enables a node to
communicate with other nodes on the link and can be used to further configure the node.
Nodes can connect to a network and automatically generate site-local and global IPv6 address without
the need for manual configuration or help of a server, such as a DHCP server. With IPv6, a router on the
link advertises in router advertisement (RA) messages any site-local and global prefixes, and its
willingness to function as a default router for the link. RA messages are sent periodically and in response
to router solicitation messages, which are sent by hosts at system startup. (See
OL-16184-01, Cisco MDS SAN-OS Release 3.x
Cisco MDS 9000 Family CLI Configuration Guide