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First Class / Second Semester/ Subject : Network & Distributed Computing/ Lecture : 8
IPv6 Features
The ability to scale networks for future demands requires a limitless supply of IP addresses; IPv6 combines expanded addressing with a more efficient and feature-rich header to meet these demands. IPv6 satisfies the increasingly complex requirements of hierarchical addressing that IPv4 does not support.
The main benefits of IPv6 include the following:
■ Larger address space: IPv6 addresses are 128 bits, compared to IPv4’s 32 bits. This larger addressing space allows more support for addressing hierarchy levels, a much greater number of addressable nodes, and simpler auto configuration of addresses.
■ Globally unique IP addresses: Every node can have a unique global IPv address, which eliminates the need for NAT.
■ Header format efficiency: A simplified header with a fixed header size makes processing more efficient.
■ Improved privacy and security: IPsec is the IETF standard for IP network security, available for both IPv4 and IPv6. Although the functions are essentially identical in both environments, IPsec is mandatory in IPv6. IPv also has optional security headers.
■ Flow labeling capability: A new capability enables the labeling of packets belonging to particular traffic flows for which the sender requests special handling, such as non default quality of service (QoS) or real-time service.
■ Increased mobility and multicast capabilities: Mobile IPv6 allows an IPv node to change its location on an IPv6 network and still maintain its existing connections. With Mobile IPv6, the mobile node is always reachable through one permanent address. A connection is established with a specific permanent address assigned to the mobile node, and the node remains connected no matter how many times it changes locations and addresses.
IPv6 Address Format
Rather than using dotted-decimal format, IPv6 addresses are written as hexadecimal numbers with colons between each set of four hexadecimal digits (which is 16 bits); we like to call this the “coloned hex” format. The format is
First Class / Second Semester/ Subject : Network & Distributed Computing/ Lecture : 8
x:x:x:x:x:x:x:x, where x is a 16-bit hexadecimal field. A sample address is as follows:
2035:0001:2BC5:0000:0000:087C:0000:000A
Note:
- We can shorten the written form of IPv6 addresses. Leading 0s within each set of four hexadecimal digits can be omitted, and a pair of colons (::) can be used, once within an address, to represent any number of successive 0s. For example, the previous address can be shortened to the following: 2035:1:2BC5::87C:0:A An all-0s address can be written as ::.
- A pair of colons (::) can be used only once within an IPv6 address. This is because an address parser identifies the number of missing 0s by separating the two parts and entering 0 until the 128 bits are complete. If two :: notations were to be placed in the address, there would be no way to identify the size of each block of 0s. Example: 3FFE: 0 501: 000 8: 0000 : 0 260:97FF:FE40:EFAB = 3FFE :5 01 :8:0:2 60:97FF:FE40:EFAB = 3FFE:501:8 :: 260:97FF:FE40:EFAB
IPv6 Addressing in an Enterprise Network
An IPv6 address consists of two parts:
- A subnet prefix representing the network to which the interface is connected. Usually 64-bits in length.
- An interface ID , sometimes called a local identifier or a token. Usually 64-bits in length.
IPv6 uses the “/prefix-length” to denote how many bits in the IPv6 address represent the subnet.
The syntax is ipv6-address/prefix-length
First Class / Second Semester/ Subject : Network & Distributed Computing/ Lecture : 8
The IPv4 header contains 12 basic header fields, followed by an options field and a data portion (which usually includes a transport layer segment). The basic IPv4 header has a fixed size of 20 octets; the variable-length options field increases the size of the total IPv4 header. IPv6 contains fields similar to 7 of the 12 IPv4 basic header fields (5 plus the source and destination address fields) but does not require the other fields.
The IPv6 header contains the following fields:
■ Version : A 4-bit field, the same as in IPv4. For IPv6, this field contains the number 6; for IPv4, this field contains the number 4. ■ Traffic class : An 8-bit field similar to the type of service (ToS) field in IPv4. This field tags the packet with a traffic class that it uses in differentiated services (DiffServ) QoS. These functions are the same for IPv6 and IPv4. ■ Flow label : This 20-bit field is new in IPv6. It can be used by the source of the packet to tag the packet as being part of a specific flow, allowing multilayer switches and routers to handle traffic on a per-flow basis rather than per- packet, for faster packet-switching performance. This field can also be used to provide QoS. ■ Payload length : This 16-bit field is similar to the IPv4 total length field. ■ Next header : The value of this 8-bit field determines the type of information that follows the basic IPv6 header. It can be transport-layer information, such as Transmission Control Protocol (TCP) or User Datagram Protocol (UDP), or it can be an extension header. The next header field is similar to the protocol field of IPv4. ■ Hop limit : This 8-bit field specifies the maximum number of hops that an IPv packet can traverse. Similar to the time to live (TTL) field in IPv4, each router decreases this field by 1. Because there is no checksum in the IPv header , an IPv6 router can decrease the field without recomputing the checksum; in IPv4 routers, the recomputation costs processing time. If this field ever reaches 0, a message is sent back to the source of the packet, and the packet is discarded. ■ Source address : This field has 16 octets (128 bits). It identifies the source of the packet. ■ Destination address : This field has 16 octets (128 bits). It identifies the destination of the packet.
First Class / Second Semester/ Subject : Network & Distributed Computing/ Lecture : 8
■ Extension headers : The extension headers, if any, and the data portion of the packet follow the other eight fields. The number of extension headers is not fixed, so the total length of the extension header chain is variable.
Special IPv6 Addresses
IPv6 Address Description
::/0 • All routes and used when specifying a default static route.
- It is equivalent to the IPv4 quad-zero (0.0.0.0).
::/128 • Unspecified address and is initially assigned to a host
when it first resolves its local link address.
::1/128 • Loopback address of local host.
- Equivalent to 127.0.0.1 in IPv4.
FE80::/10 • Link-local unicast address.
- Similar to the Windows autoconfiguration IP address of 169.254.x.x.
FF00::/8 Multicast addresses.
All other addresses
Global unicast address.
IPv6 Address Scope Types
Similar to IPv4, a single source can address datagrams to either one or many destinations at the same time in IPv6. Following are the types of IPv6 addresses:
First Class / Second Semester/ Subject : Network & Distributed Computing/ Lecture : 8
IPv6 Unicast Address
Following are the different unicast addresses that IPv6 supports:
■ Global aggregatable address (also called global unicast address)
■ Link-local address
■ IPv4-compatible IPv6 address
IPv4-to-IPv6 Transition Strategies and Deployments IPv4-to-IPv6 migration does not happen automatically. The following sections first explore the differences between IPv4 and IPv6 and then discuss possible transition strategies and deployments. Differences Between IPv4 and IPv6: Regardless of which protocol is used, the communication between IPv4 and IPv6 domains must be transparent to end users. The major differences to consider between IPv4 and IPv6 include the following: ■ IPv4 addresses are 32 bits long, whereas IPv6 addresses are 128 bits long. ■ An IPv6 packet header is different from an IPv4 packet header. The IPv6 header is longer and simpler (new fields were added to the IPv6 header, and some old fields were removed). ■ IPv6 has no concept of broadcast addresses; instead, it uses multicast addresses. ■ Routing protocols must be changed to support native IPv6 routing.
IPv4-to-IPv6 Transition The transition from IPv4 to IPv6 will take several years because of the high cost of upgrading equipment. In the meantime, IPv4 and IPv6 must coexist. The following are three primary mechanisms for the transition from IPv4 to IPv6: ■ Dual-stack : Both the IPv4 and the IPv6 stacks run on a system that can communicate with both IPv6 and IPv4 devices. ■ Tunneling : Uses encapsulation of IPv6 packets to traverse IPv4 networks, and vice versa. ■ Translation : A mechanism that translates one protocol to the other to facilitate communication between the two networks.
First Class / Second Semester/ Subject : Network & Distributed Computing/ Lecture : 8
Dual-Stack Transition Mechanism a dual-stack node enables both IPv4 and IPv6 stacks. Applications communicate with both IPv4 and IPv6 stacks; the IP version choice is based on name lookup and application preference. This is the most appropriate method for campus and access networks during the transition period, and it is the preferred technique for transitioning to IPv6. A dual-stack approach supports the maximum number of applications. Operating systems that support the IPv6 stack include FreeBSD, Linux, Sun Solaris, and Windows 2000, XP, and Vista
Tunneling Transition Mechanism The purpose of tunneling is to encapsulate packets of one type in packets of another type. When transitioning to IPv6, tunneling encapsulates IPv6 packets in IPv4 packets, as shown in the following figure.
First Class / Second Semester/ Subject : Network & Distributed Computing/ Lecture : 8
the IPv4 address that is embedded in the low-order 32 bits is used as the node’s IPv4 address. For example, the IPv4 address 192.168.30.1 would convert to the IPv4-compatible IPv6 address 0:0:0:0:0:0:192.168.30.1. Other acceptable representations for this address are ::192.168.30.1 and ::C0A8:1E01.
Dual-stack and tunneling techniques manage the interconnection of IPv6 domains. For legacy equipment that will not be upgraded to IPv6 and for some deployment scenarios, techniques are available for connecting IPv4-only nodes to IPv6-only nodes, using translation, an extension of NAT techniques. As shown in the following figure, an IPv6 node behind a translation device has full connectivity to other IPv6 nodes and uses NAT functionality to communicate with IPv4 devices.
Translation techniques are available for translating IPv4 addresses to IPv addresses and vice versa. Similar to current NAT devices, translation is done at either the transport layer or the network layer. NAT - Protocol Translation (NAT-PT) is the main translation technique; the Dual- Stack Transition Mechanism (DSTM) might also be available. The NAT-PT translation mechanism translates at the network layer between IPv4 and IPv6 addresses and allows native IPv6 hosts and applications to communicate with native IPv4 hosts and applications. An application-level gateway (ALG) translates between the IPv4 and IPv6 DNS requests and responses.
