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NOTE: You can use two colons (::) only once in an IPv6 address to represent
hexadecimal fields of consecutive zeros.
IPv6 Address Prefix
An IPv6 address prefix is a combination of an IPv6 prefix (address) and a prefix
length. The prefix takes the form ipv6-prefix/prefix-length and represents a block of
address space (or a network). The ipv6-prefix variable follows general IPv6 addressing
rules (see RFC 2373 for details). The /prefix-length variable is a decimal value that
indicates the number of contiguous, higher-order bits of the address that make up
the network portion of the address. For example, 10FA:6604:8136:6502::/64 is a
possible IPv6 prefix.
Address Types
IPv6 can use several types of addresses:
Unicast Used to identify a single interface, this release of the E Series router
product supports the following unicast address types:
Global aggregatable Provides for aggregation of routing prefixes to limit
the number of global routing table entries
Link-local Eliminates the need for a globally unique prefix. Local-link
addresses allow communications between devices on a local link.
Site-local Used as private addresses to restrict communication to a domain
portion.
NOTE: IPv6 routers must not forward packets that have site-local source or destination
addresses outside the site.
IPv4-compatible Contains a standard IPv4 address in the lower-order 32
bits of the address and zeros in the higher-order 96 bits of the address. For
example, the format of an IPv4-compatible IPv6 address is
0:0:0:0:0:0:A.B.C.D (or condensed as ::A.B.C.D). In other words, devices
using IPv6 use the entire 128-bit IPv4-compatible IPv6 address, whereas
IPv4 devices use the IPv4 address embedded within the lower-order 32-bits
of the address. You would use IPv4-compatible IPv6 addresses for devices
that must support both IPv4 and IPv6 protocols.
Multicast Used for sending packets to multiple destinations. A multicast
transmission sends packets to all interfaces that are part of a multicast group.
The group is represented by the IPv6 destination address of the packet.
Anycast – Used for a set of interfaces on different nodes. An anycast transmission
sends packets to only one of the interfaces associated with the address, not to
all of the interfaces. This interface is typically the closest interface, as defined
by the routing protocol.
Chapter 2: Configuring IPv6
129
IPv6 Overview
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