Transcript PPT
IPv6 Neil Tang 11/10/2008 CS440 Computer Networks 1 Outline Motivation New Features IPv6 Addresses Autoconfiguration Enhanced Routing Functionalities Transition from IPv4 to IPv6 CS440 Computer Networks 2 Motivation The address space of IPv4 is very limited and will be exhausted very soon. A new Internet Protocol which can provide a much larger address space is needed. CS440 Computer Networks 3 New Features Address Space: Address field is 128-bit long, i.e., about 3.41038 addresses can be supported. Auto-configuration: Hosts can automatically configure themselves such as their IP addresses. Enhanced Routing Functionalities: Routes can be selected on a packetby-packet basis. CS440 Computer Networks 4 Address Space Allocation There is no address class in IPv6. The leading bits specify different uses of IPv6 addresses. Refer to Table 4.11 in pp.320 for details. Unicast Address: This kind of addresses start with “001” and are used for unicast communications. Multicast Address: The addresses starting with “1111 1111” are used for multicast communications. IPv4 Compatible Address: An IPv4 address can be extended to an IPv6 reserved address by prefixing it with 2 bytes of “1” and then zeroextending it. CS440 Computer Networks 5 Address Notation The standard representation is x:x:x:x:x:x:x:x. Each “x” is a hexadecimal representation of a 16-bit piece of the address. E.g., 47CD:1234:4422:AC02:0022:1234:A456:0124 A large number of contiguous 0s can be written more compactly by omitting all the 0 fields. E.g., 47CD:0000:0000:0000:0000:0000:A456:0124 -> 47CD::A456:0124 A reserved IPv6 address containing an embedded IPv4 address can be represented in a special way. E.g., 128.9.33.81 -> ::FFFF:128.9.33.81. CS440 Computer Networks 6 Unicast Address IPv6 uses a classless addressing scheme. Basically, the CIDR is used to reduce routing overhead and routing table sizes. A stub and a multi-homed AS is usually considered as a subscriber. A transit AS is usually considered as a provider. There are direct providers (e.g., regional networks) and indirect providers (e.g., backbone networks) Based on CIDR, a common prefix is assigned to a provider and then the provider assigns longer prefixes to its subscribers. CS440 Computer Networks 7 Unicast Address The lengths of a particular ID field is not fixed and may be different under different situations, e.g., a provider with few subscribers might have a longer ProviderID field than one with many subscribers. 3 m n o p 125- m- n- o- p 010 RegistryID ProviderID SubscriberID SubnetID InterfaceID CS440 Computer Networks 8 IPv6 Packet Format Version: 6 for IPv6 0 Version PayloadLen: the length of the packet in terms of byte, excluding the header NextHeader: the upper layer protocol (e.g., TCP or UDP) or the next extended header. HopLimit: same as TTL 4 12 TrafficClass PayloadLen 16 24 31 Flow Label NextHeader HopLimit SourceAddress DestinationAddress Next header/data SourceAddress and DestinationAddress CS440 Computer Networks 9 Autoconfiguration After a host is attached to a network, it first obtains the network prefix by listening to the periodical advertisement Then it combines the prefix with its own physical address (e.g., a 48-bit Ethernet address) to form a valid IPv6 address. CS440 Computer Networks 10 Enhanced Routing Functionalities In IPv6, the routing header of a packet can contain a list of IPv6 addresses representing a set of routers or backbone networks that the packet should visit en route to its destination. IPv6 defines an anycast address which can be assigned to a set of routers. A packet including an anycast address will go to the nearest of those routers. CS440 Computer Networks 11 Transition from IPv4 to IPv6 Dual-Stack Operation: Each host or router runs both IPv4 protocol stack and IPv6 stack. Tunneling: The IPv6 packet is encapsulated within an IPv4 header by a tunnel endpoint and transmitted across the IPv4-only network, and then is decapsulated by the endpoint on another end. CS440 Computer Networks 12