Address Scope; Address Structure - Juniper IGP - CONFIGURATION GUIDE V11.1.X Configuration Manual

JUNOSe 11.0.x IP, IPv6, and IGP Configuration Guide
NOTE: IPv6 does not use broadcast addresses; instead, IPv6 uses multicast addresses.

Address Scope

Some unicast and multicast IPv6 addresses contain a value known as scope. This
value identifies the application suitable for the address.
Unicast addresses support two types of scope global and local. In addition, there
are two types of local scope link-local addresses and site-local addresses.
Link-local unicast addresses, identified by the first ten bits of the prefix, function
within a single network link. You cannot use link-local addresses outside a network
link.
Site-local unicast addresses function within a site or an intranet. A site consists of
multiple network links, and site-local addresses identify nodes inside the intranet.
You cannot use site-local addresses outside the site.
Multicast addresses support 16 different types of scope, including node, link, site,
organization, and global scope. A four-bit field in the prefix identifies the scope.

Address Structure

Unicast addresses identify a single interface. The address consists of n bits for the
prefix and 128-n bits for the interface ID.
Multicast addresses identify a set of interfaces. The address is made up of the first
8 bits of all ones, a 4-bit flag field, a 4-bit scope field, and a 112-bit group ID.
11111111 | flgs | scop | group ID
The first octet of ones identifies the address as a multicast address. The flags field
identifies whether the multicast address is a well-known address or whether it is a
transient multicast address. The scope field identifies the scope of the multicast
address. The 112-bit group ID identifies the multicast group.
Similar to multicast addresses, anycast addresses identify a set of interfaces. However,
packets are sent to only one of the interfaces, not to all interfaces. Anycast addresses
are allocated from the normal unicast address space and cannot be distinguished
from a unicast address in format. Therefore, each member of an anycast group must
be configured to recognize certain addresses as anycast addresses.
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IPv6 Overview
Loopback Used by a node to send an IPv6 packet to itself. An IPv6 loopback
address functions the same as an IPv4 loopback address.
Unspecified Indicates the absence of an IPv6 address. For example, newly
initialized IPv6 nodes may use the unspecified address as the source address in
their packets until they receive an IPv6 address.