Information Technology Reference
In-Depth Information
IPv6
Cisco added IPv6 to the CCIE written exam blueprint. You need to become extremely familiar
with its specifications. The driving motivation for the adoption of a new version of IP is the
limitation imposed by the 32-bit address field in IPv4. In the 1990s, there was concern that the
IP address space would be depleted soon. Although CIDR and NAT slowed down the deployment
of IPv6, its standards and potential deployments are maturing.
The IPv6 specification provides 128-bits for addressing—a significant increase from 32-bits.
The overall specification of IPv6 is in RFC 2460. Other RFCs that describe IPv6 specifications
are 2373, 2374, 2461, 2462, and 2463.
IPv6 includes the following enhancements over IPv4:
Expanded address space —IPv6 uses 128-bit addresses instead of the 32-bit addresses in
IPv4.
Improved option mechanism —IPv6 options are placed in separate optional headers that
are located between the IPv6 header and the transport-layer header.
Address autoconfiguration —This capability provides for the dynamic assignment of
IPv6 addresses.
Support for resource allocation —Instead of the ToS field in IPv4, IPv6 enables the
labeling of packets that belong to a particular traffic flow, for which the sender requests
special handling; this aids in the support of specialized traffic, such as real-time video.
Security capabilities —IPv6 includes features that support authentication and privacy.
IPv6 security is discussed in the Security section of this document.
IPv6 Address Representation
RFC 2373 specifies the IPv6 addressing architecture. IPv6 addresses are 128-bits long. IPv6
addresses are represented in hexadecimal, divided into eight 16-bit pieces. This form is
represented as follows:
X:X:X:X:X:X:X:X
Each X represents the hexadecimal digits.
An example of a full IPv6 address is FE1A:4CB9:001B:0000:0000:12D0:005B:06B0. All 0
groups can be shortened by using one 0. Multiple groups of 16-bit 0s can be represented with
a :: symbol, which can appear only once in the number. Also, leading 0s in a 16-bit piece do not
need to be represented. This sample IPv6 address can be shortened to FE1A:4CB9:1B:0:0:
12D0:5B:6B0 or FE1A:4CB9:1B::12D0:5B:6B0.
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