IPv4 vs IPv6

Introduction to IPv6

Microsoft is delivering support for the emerging update to the Internet Layer Protocol through Internet Protocol version 6 (or simply IPv6 (RFC 2460)) for packet-switched inter-networks. IPv4 is currently the dominant Internet Protocol version, and was the first to receive widespread use.

The Internet Engineering Task Force (IETF) has designated IPv6 as the successor to version 4 for general use on the Internet. It significantly increases the size of the address space used to identify communication endpoints in the Internet, thereby allowing it to continue its tremendous growth rate. IPv6 is also known as IPng (IP Next Generation).

Limitations of IPv4

Most of today's internet uses IPv4, which is now nearly twenty years old. IPv4 was remarkably but in spite of that it is beginning to have problems. Most importantly, there is a growing shortage of IPv4 addresses, which are needed by all new machines added to the Internet.

The limited address range forces organizations to use Network Address Translation (NAT) firewalls to map multiple private addresses to a single public IP address. NATs does not support standards-based network-layer security and also creates complicated barriers to VoIP, and other services.

The routing tables of Internet backbone routers are becoming larger. A separate routing table entry is needed for each network resulting in a large number of routing table entries.

Security was also an issue for IPv4. Although there are lots of ways of encrypting IPv4 traffic, such as using the IPSec protocol, but unfortunately all of the IPv4 encryption methods are proprietary and no real standard encryption methods exist.

Features of IPv6

The IPv6 header has a new header format that is designed to minimize header overhead. This optimization is achieved by moving both non-essential fields and optional fields to extension headers that appear after the IPv6 header. Intermediate routes can process the streamlined IPv6 header more efficiently. IPv4 headers and IPv6 headers do not interoperate. IPv6 is not a superset of functionality, that is backward compatible with IPv4 is not possible. A host or router must use an implementation of both IPv4 and IPv6 to recognize and process both header formats. The IPv6 header is only twice as large as the IPv4 header, even though IPv6 addresses are four times as large as IPv4 addresses.

IPv6 features a larger address space than that of IPv4. IPv6 has 128-bit (16 byte) source and destination IP addresses. Although 128 bits can express over 3.4×1038 possible combination's, the large address space of IPv6 has been designed for multiple levels of subnetting and address allocation from the Internet backbone to the individual subnets within an organization.

Multicast, the ability to send a single packet to multiple destinations, is part of the base specification in IPv6. This is unlike IPv4, where it is optional (but usually implemented). Multicasting is delivering a data stream to multiple destinations at the same time, with no duplication unless called for. Those functionalities are not supported by IPv4. The other two types of addressing that are standard practice for IPv6 are unicast and anycast. The former is a transmission from just one host to just one other host; the latter is from one host to the nearest of many hosts.

The Time-to-Live field of IPv4 has been replaced by a Hop-Limit field.

IPv6 offers a higher level of built-in security, and it has been specifically designed with mobile devices in mind. The mobility comes in the form of Mobile IP, which allows roaming between different networks without losing an established IP address. Unlike mobile IPv4, Mobile IPv6 (MIPv6) avoids triangular routing and is therefore as efficient as normal IPv6.

IPv6 can easily be extended by adding extension headers after the IPv6 header. Unlike options in the IPv4 header, which can support only 40 bytes of options, the size of IPv6 extension headers is constrained only by the size of the IPv6 packet.

Jumbograms: IPv4 limits packets to 64 KB of payload. IPv6 has optional support for packets over this limit, referred to as jumbograms, which can be as large as 4 GB. The use of jumbograms may improve performance over high-MTU networks. The presence of jumbograms is indicated by the Jumbo Payload Option header.

IPv6 also includes standardized support for QoS. The QoS implementation is set up so that routers can identify packets belonging to an individual QoS flow. Furthermore, QoS instructions are included in the IPv6 packet header. This means that the packet body can be encrypted, but QoS will still function because the header portion containing the QoS instructions is not encrypted. This will make it possible to send streaming audio and video over the Internet with IPSec encryption, but in a manner that guarantees adequate bandwidth for real-time playback.

Difference Between IPv4 and IPv6

IPv4

• Source and destination addresses are 32 bits (4 bytes) in length.
• IPSec support is optional.
• IPv4 header does not identify packet flow for QoS handling by routers.
• Both routers and the sending host fragment packets.
• Header includes a checksum.
• Header includes options.
• Address Resolution Protocol (ARP) uses broadcast ARP Request frames to resolve an IP address to a link-layer address.
• Internet Group Management Protocol (IGMP) manages membership in local subnet groups.
• ICMP Router Discovery is used to determine the IPv4 address of the best default gateway, and it is optional.
• Broadcast addresses are used to send traffic to all nodes on a subnet.
• Must be configured either manually or through DHCP.
• Uses host address (A) resource records in Domain Name System (DNS) to map host names to IPv4 addresses.
• Uses pointer (PTR) resource records in the IN-ADDR.ARPA DNS domain to map IPv4 addresses to host names.
• Must support a 576-byte packet size (possibly fragmented).

IPv6

• Source and destination addresses are 128 bits (16 bytes) in length.
• IPSec support is required.
• IPv6 header contains Flow Label field, which identifies packet flow for QoS handling by router.
• Only the sending host fragments packets; routers do not.
• Header does not include a checksum.
• All optional data is moved to IPv6 extension headers.
• Multicast Neighbor Solicitation messages resolve IP addresses to link-layer addresses.
• Multicast Listener Discovery (MLD) messages manage membership in local subnet groups.
• ICMPv6 Router Solicitation and Router Advertisement messages are used to determine the IP address of the best default gateway, and they are required.
• IPv6 uses a link-local scope all-nodes multicast address.
• Does not require manual configuration or DHCP.
• Uses host address (AAAA) resource records in DNS to map host names to IPv6 addresses.
• Uses pointer (PTR) resource records in the IP6.ARPA DNS domain to map IPv6 addresses to host names.
• Must support a 1280-byte packet size (without fragmentation).

IPv6 Header

http://gallery.techarena.in/data/516/IPv6_Header.JPG

IPv6 header contains the following things:

• Version - This field contains the version of the IP used in the packet. It is of 4-bit in IP version 6.
• Traffic class - This is an 8-bits field determining the packet priority. Priority values subdivide into ranges: traffic where the source provides congestion control and non-congestion control traffic.
• Flow label - This 20 bits specifies the QoS management. Originally created for giving real-time applications special service, but currently unused.
• Payload length - This 16 bits determines the payload length in bytes. When cleared to zero, the option is a "Jumbo payload" (hop-by-hop).
• Next header - This 8-bits field specifies the next encapsulated protocol. The values are compatible with those specified for the IPv4 protocol field.
• Hop limit - This is an 8-bits field newly introduced in IPv6. It replaces the time to live field of IPv4.
• Source Address - This 128 bits field determines the logical address of the host that is sending the packet.
• Destination Address - This 128 bits field determines the logical address of the host that is receiving the packet.

The payload can have a size of up to 64KB in standard mode, or larger with a "jumbo payload" option.

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