IPv6 Addressing Overview

IP version 6 (IPv6) increases the size of the IP address from the 32 bits found in IPv4 to 128 bits. This increased size provides for a broader range of addressing hierarchies and a much larger number of addressable nodes.

In addition to the increased size, IPv6 addresses can be of different scopes that categorize what types of applications are suitable for the address. IPv6 does not support broadcast addresses, but uses multicast addresses to serve this role. In addition, IPv6 also defines a new type of address called anycast.

This topic describes the following:

Address Representation

IPv6 addresses consist of eight hexadecimal groups. Each hexadecimal group, separated by a colon (:), consists of a 16-bit hexadecimal value. The following is an example of the IPv6 format:


A group of xxxx represents the 16-bit hexadecimal value. Each individual x represents a 4-bit hexadecimal value. The following is an example of a possible IPv6 address:


Note: Hexadecimal letters in IPv6 addresses are not case sensitive.

This section explains the following:

IPv6 Address Compression

IPv6 addresses often contain consecutive hexadecimal fields of zeros. To simplify address entry, you can use two colons (::) to represent the consecutive fields of zeros when typing the IPv6 address. Table 35 provides compressed IPv6 address format examples.

Table 35: Compressed IPv6 Formats

IPv6 Address Type

Full Format

Compressed Format













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:

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.

ICMP Support

Internet Control Message Protocol (ICMP) provides a mechanism that enables a router or destination host to report an error in data traffic processing to the original source of the packet. For this release, the E Series router supports ICMP for use in the IPv6 ping and traceroute commands.

The ping and traceroute commands help you determine destination reachability within a network.

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