TCP/IPv6 Configuration and Management Manual (G06.24+)

IPv6 Fundamentals
HP NonStop TCP/IPv6 Configuration and Management Manual—524523-008
A-12
Address Lifetimes
information with Domain Name System (DNS) servers, these mechanisms provide a
path toward network renumbering and provide network administrators with control over
the use of network addresses without manual intervention on each host on the
network.
Address Lifetimes
IPv6 addresses are leased to an interface for a fixed (possibly infinite) length of time.
Each address has an associated lifetime that indicates how long the address is bound
to an interface. When a lifetime expires, the binding (and address) become invalid and
the address can be reassigned to another interface elsewhere in the Internet. To
handle the expiration of address bindings gracefully, an address goes through two
distinct phases while assigned to an interface. Initially, an address is preferred,
meaning that its use in arbitrary communication is unrestricted. Later, an address
becomes deprecated in anticipation that its current interface binding will become
invalid. While in a deprecated state, the use of an address is discouraged, but not
strictly forbidden. New communication (for example, the opening of a new TCP
connection) should use a preferred address when possible. A deprecated address
should be used only by applications that have been using it and would have difficulty
switching to another address without a service disruption.
Stateless Address Autoconfiguration Behavior
The autoconfiguration process specified in this subsection applies only to hosts and
not routers. As host autoconfiguration uses information advertised by routers, this
subsection assumes that a router that supports the Neighbor Discovery Protocol is
configured on the network.
To insure that all configured addresses are likely to be unique on a given link, nodes
run a duplicate-address detection algorithm on all addresses before assigning them to
an interface.
Autoconfiguration is performed only on multicast-capable links and begins when a
multicast-capable interface is enabled. Nodes (both hosts and routers) begin the
autoconfiguration process by generating a link-local address for the interface. A link-
local address is formed by appending the interface's identifier to the well-known link-
local prefix.
Before the link-local address can be assigned to an interface and used, however, a
node must attempt to verify that this tentative address is not already in use by another
node on the link. Specifically, the node sends a neighbor solicitation message
containing the tentative address as the target. If another node is already using that
address, that node returns a neighbor advertisement saying so. If another node is also
attempting to use the same address, that node sends a neighbor solicitation for the
target as well. The exact number of times the neighbor solicitation is (re)transmitted
and the delay time between consecutive solicitations is link-specific and can be set by
system management. In the NonStop TCP/IPv6 subsystem, the IPV6DADRETRIES int
on page 8-32 attribute and the IPV6RETRANSMITIMER int on page 8-32 attribute
affect these behaviors.