To comprehend the IP addressing issues facing network administrators today, consider that the IPv4 address space provides approximately 4,294,967,296 unique addresses. Of these, only 3.7 billion addresses are assignable because the IPv4 addressing system separates the addresses into classes and reserves addresses for multicasting, testing, and other specific uses.
Based on figures as recent as January 2007, about 2.4 billion of the available IPv4 addresses are already assigned to end users or ISPs. That leaves roughly 1.3 billion addresses still available from the IPv4 address space. Despite this seemingly large number, IPv4 address space is running out.
Over the past decade, the Internet community has analyzed IPv4 address exhaustion and published mountains of reports. Some reports predict IPv4 address exhaustion by 2010, and others say it will not happen until 2013. The growth of the Internet, matched by increasing computing power, has extended the reach of IP-based applications.
The pool of numbers is shrinking for the following reasons:
Population growth - The Internet population is growing. In November 2005, Cisco estimated that there were approximately 973 million users. This number has doubled since then. In addition, users stay on longer, reserving IP addresses for longer periods and are contacting more and more peers daily.
Mobile users - Industry has delivered more than one billion mobile phones. More than 20 million IP-enabled mobile devices, including personal digital assistants (PDAs), pen tablets, notepads, and barcode readers, have been delivered. More and more IP-enabled mobile devices are coming online every day. Old mobile phones did not need IP addresses, but new ones do.
Transportation - There will be more than one billion automobiles by 2008. Newer models are IP-enabled to allow remote monitoring to provide timely maintenance and support. Lufthansa already provides Internet connectivity on their flights. More carriers, including ships at sea, will provide similar services.
Consumer electronics - The newest home appliances allow remote monitoring using IP technology. Digital Video Recorders (DVRs) that download and update program guides from the Internet are an example. Home networking can connect these appliances.
IP Structure.PNG
The ability to scale networks for future demands needs a limitless supply of IP addresses and improved mobility that DHCP and NAT alone cannot meet. IPv6 satisfies the increasingly complex requirements of hierarchical addressing that IPv4 does not provide.
Given the huge installed base of IPv4 in the world, it is not difficult to appreciate that transitioning to IPv6 from IPv4 deployments is a challenge. There are, however, a variety of techniques, including an auto-configuration option, to make the transition easier. The transition mechanism you use depends on the needs of your network.
The figure compares the binary and alphanumeric representations of IPv4 and IPv6 addresses. An IPv6 address is a 128-bit binary value, which can be displayed as 32 hexadecimal digits. IPv6 should provide sufficient addresses for future Internet growth needs for many years to come. There are enough IPv6 addresses to allocate more than the entire IPv4 Internet address space to everyone on the planet.
2. The history and the current technology
IPv6 would not exist were it not for the recognized depletion of available IPv4 addresses. However, beyond the increased IP address space, the development of IPv6 has presented opportunities to apply lessons learned from the limitations of IPv4 to create a protocol with new and improved features.
A simplified header architecture and protocol operation translates into reduced operational expenses. Built-in security features mean easier security practices that are sorely lacking in many current networks. However, perhaps the most significant improvement offered by IPv6 is the address auto-configuration features it has.
Address auto-configuration also means more robust plug-and-play network connectivity. Auto-configuration supports consumers who can have any combination of computers, printers, digital cameras, digital radios, IP phones, Internet-enabled household appliances, and robotic toys connected to their home networks. Many manufacturers already integrate IPv6 into their products.
Many of the enhancements that IPv6 offers are explained in this section, including:
Enhanced IP addressing
Simplified header
Mobility and security
Transition richness
2.1 Enhanced IP Addressing
A larger address space offers several enhancements, including:
Improved global reachability and flexibility.
Better aggregation of IP prefixes announced in routing tables. Multihomed hosts. Multihoming is a technique to increase the reliability of the Internet connection of an IP network. With IPv6, a host can have multiple IP addresses over one physical upstream link. For example, a host can connect to several ISPs.
Auto-configuration that can include data link layer addresses in the address space.
More plug-and-play options for more devices.
Public-to-private, end-to-end readdressing without address translation. This makes peer-to-peer (P2P) networking more functional and easier to deploy.
Simplified mechanisms for address renumbering and modification.
Headers.PNG2.2 Simplified Header
The figure compares the simplified IPv6 header structure to the IPv4 header. The IPv4 header has 20 octets and 12 basic header fields, followed by an options field and a data portion. The IPv6 header has 40 octets, three IPv4 basic header fields, and five additional header fields.
The IPv6 simplified header offers several advantages over IPv4:
Better routing efficiency for performance and forwarding-rate scalability
No broadcasts and thus no potential threat of broadcast storms
No requirement for processing checksums
Simplified and more efficient extension header mechanisms
Flow labels for per-flow processing with no need to open the transport inner packet to identify the various traffic flows
2.3 Enhanced Mobility and Security
Mobility and security help certain compliance with mobile IP and IP Security (IPsec) standards functionality. Mobility enables people with mobile network devices-many with wireless connectivity-to move around in networks.
The IETF Mobile IP standard is available for both IPv4 and IPv6. The standard enables mobile devices to move without breaks in established network connections. Mobile devices use a home address and a care-of address to achieve this mobility. With IPv4, these addresses are manually configured. With IPv6, the configurations are dynamic, giving Ipv6-enabled devices built-in mobility.
IPsec is useable for both IPv4 and IPv6. Although the functionalities are essentially identical in both, IPsec is required in IPv6, making the IPv6 Internet more secure.
3. IPv6 Addressing
3.1IPv6 Address Representation
Everybody knows the 32-bit IPv4 address as a series of four 8-bit fields, separated by dots. However, larger 128-bit IPv6 addresses need a different representation because of their size. IPv6 addresses use colons to separate entries in a series of 16-bit hexadecimal.
Address Representation 1.PNG
Address Representation 2.PNG
The figure shows the address 2031:0000:130F:0000:0000:09C0:876A:130B. IPv6 does not require explicit address string notation. The figure shows how to shorten the address by applying the following guidelines:
Leading zeros in a field are optional. For example, the field 09C0 equals 9C0, and the field 0000 equals 0. So 2031:0000:130F:0000:0000:09C0:876A:130B can be written as 2031:0:130F:0000:0000:9C0:876A:130B.
Successive fields of zeros can be represented as two colons "::". However, this shorthand method can only be used once in an address. For example 2031:0:130F:0000:0000:9C0:876A:130B can be written as 2031:0:130F::9C0:876A:130B.
An unspecified address is written as "::" because it contains only zeros.
Using the "::" notation greatly reduces the size of most addresses as shown. An address parser identifies the number of missing zeros by separating any two parts of an address and entering 0s until the 128 bits are complete.
3.2 IPv6 Addresses
3.2.1 IPv6 Global Unicast Address
IPv6 addresses.PNG
IPv6 has an address format that enables aggregation upward eventually to the ISP. Global unicast addresses typically consists of a 48-bit global routing prefix and a 16-bit subnet ID. Individual organizations can use a 16-bit subnet field to create their own local addressing hierarchy. This field allows an organization to use up to 65,535 individual subnets.
At the top of the figure, it can be seen how additional hierarchy is added to the 48-bit global routing prefix with the registry prefix, ISP Prefix, and site prefix. The current global unicast address that is assigned by the IANA uses the range of addresses that start with binary value 001 (2000::/3), which is 1/8 of the total IPv6 address space and is the largest block of assigned addresses. The IANA is allocating the IPv6 address space in the ranges of 2001::/16 to the five RIR registries (ARIN, RIPE, APNIC, LACNIC, and AfriNIC).
3.2.2 Reserved Addresses
The IETF reserves a portion of the IPv6 address space for various uses, both present and future. Reserved addresses represent 1/256th of the total IPv6 address space. Some of the other types of IPv6 addresses come from this block.
3.2.3 Private Addresses
A block of IPv6 addresses is set aside for private addresses, just as is done in IPv4. These private addresses are local only to a particular link or site, and are therefore never routed outside of a particular company network. Private addresses have a first octet value of "FE" in hexadecimal notation, with the next hexadecimal digit being a value from 8 to F.
These addresses are further divided into two types, based upon their scope.
Site-local addresses, are addresses similar to the RFC 1918 Address Allocation for Private Internets in IPv4 today. The scope of these addresses is an entire site or organization. However, the use of site-local addresses is problematic and is being deprecated as of 2003 by RFC 3879. In hexadecimal, site-local addresses begin with "FE" and then "C" to "F" for the third hexadecimal digit. So, these addresses begin with "FEC", "FED", "FEE", or "FEF".
Link-local addresses, are new to the concept of addressing with IP in the Network layer. These addresses have a smaller scope than site-local addresses; they refer only to a particular physical link (physical network). Routers do not forward datagrams using link-local addresses at all, not even within the organization; they are only for local communication on a particular physical network segment. They are used for link communications such as automatic address configuration, neighbor discovery, and router discovery. Many IPv6 routing protocols also use link-local addresses. Link-local addresses begin with "FE" and then have a value from "8" to "B" for the third hexadecimal digit. So, these addresses start with "FE8", "FE9", "FEA", or "FEB".
3.2.4 Loopback Address
Just as in IPv4, a provision has been made for a special loopback IPv6 address for testing; datagrams sent to this address "loop back" to the sending device. However, in IPv6 there is just one address, not a whole block, for this function. The loopback address is 0:0:0:0:0:0:0:1, which is normally expressed using zero compression as "::1".
3.2.5 Unspecified Address
In IPv4, an IP address of all zeroes has a special meaning; it refers to the host itself, and is used when a device does not know its own address. In IPv6, this concept has been formalized, and the all-zeroes address (0:0:0:0:0:0:0:0) is named the "unspecified" address. It is typically used in the source field of a datagram that is sent by a device that seeks to have its IP address configured. You can apply address compression to this address; because the address is all zeroes, the address becomes just "::".
3.3 IPv6 Address Management
IPv6 addresses use interface identifiers to identify interfaces on a link. Think of them as the host portion of an IPv6 address. Interface identifiers are required to be unique on a specific link. Interface identifiers are always 64 bits and can be dynamically derived from a Layer 2 address (MAC).
We can assign an IPv6 address ID statically or dynamically:
Static assignment using a manual interface ID
Static assignment using an EUI-64 interface ID
Stateless auto-configuration
DHCP for IPv6 (DHCPv6)
3.3.1 Manual Interface ID Assignment
One way to statically assign an IPv6 address to a device is to manually assign both the prefix (network) and interface ID (host) portion of the IPv6 address. To configure an IPv6 address on a Cisco router interface, use the ipv6 address ipv6-address/prefix-length command in interface configuration mode. The following example shows the assignment of an IPv6 address to the interface of a Cisco router:
RouterX(config-if)#ipv6 address 2001:DB8:2222:7272::72/64
3.3.2 EUI-64 Interface ID Assignment
Another way to assign an IPv6 address is to configure the prefix (network) portion of the IPv6 address and derive the interface ID (host) portion from the Layer 2 MAC address of the device, which is known as the EUI-64 interface ID.
EUI 64.PNG
The EUI-64 standard explains how to stretch IEEE 802 MAC addresses from 48 to 64 bits by inserting the 16-bit 0xFFFE in the middle at the 24th bit of the MAC address to create a 64-bit, unique interface identifier.
To configure an IPv6 address on a Cisco router interface and enable IPv6 processing using EUI-64 on that interface, use the ipv6 address ipv6-prefix/prefix-length eui-64 command in interface configuration mode. The following example shows the assignment of an EUI-64 address to the interface of a Cisco router:
RouterX(config-if)#ipv6 address 2001:DB8:2222:7272::/64 eui-64
3.3.3 Stateless Auto-configuration
Auto-configuration automatically configures the IPv6 address. In IPv6, it is assumed that non-PC devices, as well as computer terminals, will be connected to the network. The auto-configuration mechanism was introduced to enable plug-and-play networking of these devices to help reduce administration overhead.
3.3.4 DHCPv6 (Stateful)
DHCPv6 enables DHCP servers to pass configuration parameters, such as IPv6 network addresses, to IPv6 nodes. It offers the capability of automatic allocation of reusable network addresses and additional configuration flexibility. This protocol is a stateful counterpart to IPv6 stateless address auto-configuration (RFC 2462), and can be used separately or concurrently with IPv6 stateless address auto-configuration to obtain configuration parameters.
4. IPv6 Transition Strategies
The transition from IPv4 doesn’t need upgrades on all nodes at the same time. Many transition mechanisms enable smooth integration of IPv4 and IPv6. Other mechanisms that provide IPv4 nodes to communicate with IPv6 nodes are available. Different situations demand different strategies. The figure illustrates the richness of available transition strategies.
The most common techniques to transition from IPv4 to IPv6 are:
Dual Stacking and
Tunneling
4.1 Dual Stacking
Dual stacking is an integration method in which a node has implementation and connectivity to both an IPv4 and IPv6 network. This is the recommended option and involves running IPv4 and IPv6 at the same time. Router and switches are configured to support both protocols, with IPv6 being the preferred protocol.
4.2 Tunneling
The second major transition technique is tunneling. There are several tunneling techniques available, including:
Manual IPv6-over-IPv4 tunneling - An IPv6 packet is encapsulated within the IPv4 protocol. This method requires dual-stack routers.
Dynamic 6to4 tunneling - Automatically establishes the connection of IPv6 islands through an IPv4 network, typically the Internet. It dynamically applies a valid, unique IPv6 prefix to each IPv6 island, which enables the fast deployment of IPv6 in a corporate network without address retrieval from the ISPs or registries.
Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) tunneling - Automatic overlay tunneling mechanism that uses the underlying IPv4 network as a link layer for IPv6. ISATAP tunnels allow individual IPv4 or IPv6 dual-stack hosts within a site to communicate with other such hosts on a virtual link, creating an IPv6 network using the IPv4 infrastructure.
Teredo tunneling - An IPv6 transition technology that provides host-to-host automatic tunneling instead of gateway tunneling. This approach passes unicast IPv6 traffic when dual-stacked hosts (hosts that are running both IPv6 and IPv4) are located behind one or multiple IPv4 NATs.
Transition Strategies.PNG
5. Routing Considerations with IPv6
Like IPv4 classless inter-domain routing (CIDR), IPv6 uses longest prefix match routing. IPv6 uses modified versions of most of the common routing protocols to handle longer IPv6 addresses and different header structures.
Larger address spaces make room for large address allocations to ISPs and organizations. An ISP aggregates all of the prefixes of its customers into a single prefix and announces the single prefix to the IPv6 Internet. The increased address space is sufficient to allow organizations to define a single prefix for their entire network.
But how does this affect router performance? A brief review of how a router functions in a network helps illustrate how IPv6 affects routing. Conceptually, a router has three functional areas:
The control plane handles the interaction of the router with the other network elements, providing the information needed to make decisions and control the overall router operation. This plane runs processes such as routing protocols and network management. These functions are generally complex.
The data plane handles packet forwarding from one physical or logical interface to another. It involves different switching mechanisms such as process switching and Cisco Express Forwarding (CEF) on Cisco IOS software routers.
Enhanced services include advanced features applied when forwarding data, such as packet filtering, quality of service (QoS), encryption, translation, and accounting.
IPv6 presents each of these functions with specific new challenges.
5.1 IPv6 Control Plane
Enabling IPv6 on a router starts its control plane operating processes specifically for IPv6. Protocol characteristics shape the performance of these processes and the amount of resources necessary to operate them:
IPv6 address size - Address size affects the information-processing functions of a router. Systems using a 64-bit CPU, bus, or memory structure can pass both the IPv4 source and destination address in a single processing cycle. For IPv6, the source and destination addresses require two cycles each-four cycles to process source and destination address information. As a result, routers relying exclusively on software processing are likely to perform slower than when in an IPv4 environment.
Multiple IPv6 node addresses - Because IPv6 nodes can use several IPv6 unicast addresses, memory consumption of the Neighbor Discovery cache may be affected.
IPv6 routing protocols - IPv6 routing protocols are similar to their IPv4 counterparts, but since an IPv6 prefix is four times larger than an IPv4 prefix, routing updates have to carry more information.
Routing table Size -Increased IPv6 address space leads to larger networks and a much larger Internet. This implies larger routing tables and higher memory requirements to support them.
5.2 IPv6 Data Plane
The data plane forwards IP packets based on the decisions made by the control plane. The forwarding engine parses the relevant IP packet information and does a lookup to match the parsed information against the forwarding policies defined by the control plane. IPv6 affects the performance of parsing and lookup functions:
Parsing IPv6 extension headers - Applications, including mobile IPv6, often use IPv6 address information in extension headers, thus increasing their size. These additional fields require additional processing
IPv6 address lookup - IPv6 performs a lookup on packets entering the router to find the correct output interface. In IPv4, the forwarding decision process parses a 32-bit destination address. In IPv6, the forwarding decision could conceivably require parsing a 128-bit address.
Routing Considerations.PNG
6. Configuring IPv6 Addresses
6.1 Enabling IPv6 on Cisco Routers
There are two basic steps to activate IPv6 on a router. First, you must activate IPv6 traffic-forwarding on the router, and then you must configure each interface that requires IPv6. By default, IPv6 traffic-forwarding is disabled on a Cisco router. To activate it between interfaces, you must configure the global command ipv6 unicast-routing.
The ipv6 address command can configure a global IPv6 address. The link-local address is automatically configured when an address is assigned to the interface. You must specify the entire 128-bit IPv6 address or specify to use the 64-bit prefix by using the eui-64 option.
enabling IPv6 on Cisco.PNG
6.2 IPv6 Address Configuration Example
We can completely specify the IPv6 address or compute the host identifier (rightmost 64 bits) from the EUI-64 identifier of the interface. In the example, the IPv6 address of the interface is configured using the EUI-64 format. Alternatively, you can completely specify the entire IPv6 address to assign a router interface an address using the ipv6 addressipv6-address/prefix-length command in interface configuration mode. Configuring an IPv6 address on an interface automatically configures the link-local address for that interface.
IPv6 Cnfiguration example.PNG
6.3 Cisco IOS IPv6 Name Resolution
There are two ways to perform name resolution from the Cisco IOS software process:
Define a static name for an IPv6 address using the ipv6 host name [port] ipv6-address1 [ipv6-address2...ipv6-address4] command. You can define up to four IPv6 addresses for one hostname. The port option refers to the Telnet port to be used for the associated host.
Specify the DNS server used by the router with the ip name-serveraddress command. The address can be an IPv4 or IPv6 address. You can specify up to six DNS servers with this command.
IPv6 Name resolution on Cisco IOS.PNG
