Juniper ACX1000 Configuration Manual page 592

ACX Series Universal Access Router Configuration Guide
534
Neighbor Discovery
The Neighbor Discovery protocol facilitates a substantial number of functions related
to local network connectivity, datagram routing, and configuration. Both regular hosts
and routers in an IPv6 environment count on the Neighbor Discovery protocol to
facilitate the important exchanges of information that are necessary for proper
internetwork operations. Neighbor Discovery is a messaging protocol similar to ICMP.
The following functions are performed by the protocol:
Router discovery—How a host locates routers residing on an attached link.
Prefix discovery—How a host discovers address prefixes for destinations residing on
an attached link. Nodes use prefixes to distinguish between destinations that reside
on an attached link and those destinations that it can reach only through a router.
Parameter discovery—How a node learns various parameters (link parameters or
Internet parameters) that it places in outgoing packets.
Address resolution—How a node uses only a destination IPv6 address to determine
a link-layer address for destinations on an attached link.
Next-hop determination—The algorithm that a node uses for mapping an IPv6
destination address into a neighbor IPv6 address (either the next router hop or the
destination itself) to which it plans to send traffic for the destination.
Neighbor unreachability detection—How a node determines that it can no longer
reach a neighbor.
Duplicate address detection—How a node determines whether an address is already
in use by another node.
Internet Control Message Protocol v6 (ICMPv6)
ICMP sends error messages and information messages related to IP operations. ICMPv6
defines additional error messages and informational messages specific to IPv6.
There are four different ICMPv6 error messages:
Destination Unreachable—A packet cannot be delivered due to an inherent problem
with how it is being sent. Includes a code that indicates the nature of the problem
that caused the packet not to be delivered
Packet Too Big—Sent when a packet is too large to be delivered.
Time Exceeded—A packet cannot be delivered because it has exceeded the hop
count specified in the basic header hop-by-hop field.
Parameter Problem—Indicates a problem with a field in the IPv6 header or extension
headers that makes it impossible to process the packet.
ICMPv6 information messages are used for sharing the information required to
implement various test, diagnostic, and support functions that are critical to the
operation of IPv6. There are a total of eight different ICMPv6 informational messages:
Echo Request—
Echo Reply—
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