Internet version 6 Perfo

The neighbor discovery protocol enables IPv6 nodes and routers to determine the link-layer address of a neighbor on the same network, and to find and track neighbors. The IPv6 neighbor discovery process uses IPv6 ICMP (ICMPv6) messages and solicited-node multicast addresses to determine the link-layer address of a neighbor on the same network, verify the reachability of a neighbor, and keep track of neighbor routers.

When a node wants to determine the linklayer address of another node on the same local link, a neighbor solicitation message is sent on the local link, carrying the sender own link-layer address. After receiving the neighbor solicitation message, the destination node replies by sending a neighbor advertisement message with its own link-layer address on the local link. After the neighbor advertisement is received, the source and destination nodes can communicate. Neighbor advertisement messages are also sent when there is a change in the link-layer address of a node on a local link.

To discover the routers on the local link, the IPv6 router discovery process uses router advertisement and solicitation messages. Router advertisements messages are sent out periodically on each configured interface of an IPv6 router, and also in response to router solicitation messages from IPv6 nodes on the link. When a host does not have a configured unicast address, it sends a router solicitation message, enabling the host to autoconfigure itself quickly without having to wait for the next scheduled router advertisement message.

A router advertisement contains or determines:The type of autoconfiguration a node should use ?stateless or stateful. The Hop limit value a node should place in the IPv6 header. The network prefix a node should use to form the unicast address. The maximum transmission unit (MTU) size a node should use in sending packets. Whether the originating router should be used as default router.
Stateless autoconfiguration enables serverless basic configuration of IPv6 nodes and easy renumbering. Stateless autoconfiguration uses the network prefix information in the router advertisement messages as the /64 of prefix of the node address. The remaining 64 bits address is obtained by the MAC address assigned to the Ethernet interface combined with additional bits in EUI-64 format. For instance, a node with Ethernet interface address 0003B61A2061, combined with network prefix 2001:0001:1EEF:0000/64 provided by router advertisement, will have an IPv6 address as 2001:0001:1EEF:0000:0003:B6FF:FE1A: 2061.

Renumbering of IPv6 nodes is possible through router advertisement messages, which contain both the old and new prefix. A decrease in the lifetime value of the old prefix alerts the nodes to use the new prefix, while still keeping their current connections intact with the old prefix. During this period, nodes have two unicast addresses in use. When the old prefix is no longer usable, the router advertisements will include only the new prefix.



IPv6 routers do not handle fragmentation of packets, which is done, when necessary, by the originating or source node of the packet. IPv6 uses ICMP error reports to determine whether the packet size matches the MTU size along the delivery path. When a node reports 損acket too big?via an ICMP error report, the source node will reduce the size of the transmit packet. The process is repeated until there is no 損acket too big?error along the delivery path. This allows a node to dynamically discover and adjust to differences in the MTU size of every link along a given data path.



In addition to stateless autoconfiguration, IPv6 also supports stateful configuration with DHCPv6. The IPv6 node has an option to solicit an address via DHCP server when a router is not found. The operation of DHCPv6 is mostly similar to that of DHCPv4; however, DHCPv6 uses multicast for many of its messages. IPv6 also introduces a new record type to accommodate IPv6 addresses in Domain Name Servers. The AAAA record, also known as 搎uad A? has been recommended by the IETF for mapping a host name to an IPv6 address.


IPv6 provides many benefits over legacy IPv4 technology; however, all agree that any successful strategy for IPv6 deployment requires it to coexist with IPv4 for some extended period of time. A number of strategies have been developed for managing this complex and prolonged transition from IPv4 to IPv6. The following subsections describe several of these strategies.
Dual-stack backbone


In dual-stack backbone deployment, all routers in the network maintain both IPv4 and IPv6 protocol stacks. Applications choose between using IPv4 or IPv6, with the application selecting the correct address based on the type of IP traffic and particular requirements of the communication.

Today, dual-stack routing is the preferred deployment strategy for network infrastructures with a mixture of IPv4 and IPv6 applications that require both protocols. This strategy has several limitations, however: all routers in the network must be upgraded to IPv6; routers also require a dual addressing scheme, dual management of the IPv4 and IPv6 routing protocols and sufficient memory for both the IPv4 and IPv6 routing tables.
IPv6 over IPv4 tunneling
IPv6 over IPv4 tunneling encapsulates IPv6 traffic within IPv4 packets, to be sent over an IPv4 backbone (Figure 8). This enables 搃sland?IPv6 end systems and routers to communicate through an existing IPv4 infrastructure.

A variety of tunneling mechanisms are available for deploying IPv6 (Figure 9), as described in the following sections.

Manually configured tunnels. As defined by RFC 2893, both end points of the tunnel need to be configured with appropriate IPv6 and IPv4 addresses. The edge routers sitting at the end points, usually a dual stack router, will forward the tunneled traffic based on the configuration.

GRE (Generic Routing Encapsulation) tunnels. Defined to transport data over the IPv4 network, GRE allows one network protocol to be transmitted over another network protocol, by encapsulating the packets to be transmitted within GRE packets. GRE is an ideal mechanism to tunnel IPv6 traffic.

 

 

 

 

. IPv6 tunnel mechanisms.

IPv4-compatible tunnels or 6over4 tunnels. As defined in RFC 2893, these tunnel mechanisms automatically set up tunnels based on the IPv4-compatible IPv6 addresses. An IPv4-compatible IPv6 address defines the left-most 96 bits as zero, followed by an IPv4 address embedded in the last 32 bits. For example, 0:0:0:0:0:0.64.23.45.21 is an IPv4- compatible address.

As defined by RFC 3056, 6to4 tunneling uses an IPv4 address embedded in the IPv6 address to identify the end point of the tunnel and setup tunnel automatically (Figure 10).

ISATAP (Intra-Site Automatic Tunnel Addressing Protocol) tunnels. As defined in draft-ietfngtrans- isatap-16, ISATAP tunneling is very similar to 6to4 tunneling, but is designed for use in a local site or campus network. The ISATAP address contains the 64-bit network prefix, 0000:5EFE, and an IPv4 address identifying the address of the tunnel end point (Figure 11).

 

 

 

 

. ISATAP tunneling address format.

MPLS (Multi-Protocol Label Switching) tunnels. Using MPLS technology, isolated IPv6 domains can communicate with each other over a MPLS IPv4 core network. Because MPLS forwarding is based on labels rather than the IP header itself, this implementation requires far fewer backbone infrastructure upgrades and less reconfiguration of core routers, providing a very cost-effective way to deploy IPv6. Additionally, MPLS抯 inherent VPN and traffic engineering services allow IPv6 networks to be combined into VPNs or extranets over an infrastructure supporting IPv4 VPNs and MPLS-TE.

Expectations for IPv6 are high: it is perceived as the protocol of the next generation Internet, replacing today legacy IPv4-based networks. As described above, IPv6 deploys a new data plane to fix various addressing and efficiency problems with IPv4, and a new routing control plane to effectively make use of the new addresses. The impact of the new data and control planes on today抯 networks is significant. Failures or interruption are unacceptable in missioncritical networking environments. Network operators and service providers are facing tough questions ?when and how to migrate to IPv6? To answer these questions with certainty, they need assurance that in their particular networks, IPv6 will provide:

Rapid expansion needed for more users and devices. Smooth transition and coexistence with IPv4. Deliverable Quality of Service.

Network equipment manufacturers (NEMs) face the challenge of building routers to support both IPv6 and IPv4 networks, with two sets of control and data planes. This can add significant resource requirements to routers supporting dual stacks, impacting router performance and scalability. Additional transition mechanisms like tunneling and application/address translation add complexity to router design.

For end users, IPv6 improves productivity by enabling network connectivity via a wider range of media and delivery mechanisms. But for general acceptance, the new IPv6 networks must demonstrate responsiveness at least equal to that of IPv4. In addition, while several end user environments and applications like Windows XP, Linux, and sendmail support IPv6 today, more applications are needed to enhance IPv6 overall acceptance.