CSC 600Internetworking

withTCP/IPUnit 7: IPv6

(ch. 33)

Dr. Cheer-Sun Yang

Spring 2001

IP v6 - Version Number

• IP v 1-3 defined and replaced

• IP v4 - current version

• IP v5 - streams protocol

• IP v6 - replacement for IP v4– During development it was called IPng – Next Generation

Why Change IP?

• New computer and communication technologies

• New applications – VoIP requires real-time data delivery

• Increase in size and load – too many hosts!

Why Change IP?

• Address space exhaustion– Two level addressing (network and host) wastes space

– Network addresses used even if not connected to Internet

– Growth of networks and the Internet

– Extended use of TCP/IP

– Single address per host

• Requirements for new types of service

Why Change IP?

• New technologies : since 1970s,– processor performance has increased over two orders

of magnitude– Memory sizes have increased by over a factor of 100– Network bandwidth of the Internet backbone has

risen by a factor of 7000– LAN technologies have emerged

• Increase in size – the number of hosts has risen from a handful to 56 million; the current 32-bit IP address space cannot accommodate projected growth of the global Internet beyond 2002.

IPv6 RFCs

• 1752 - Recommendations for the IP Next Generation Protocol

• 2460 - Overall specification

• 2373 - addressing structure

• Others : 2462, 2463, 2464, 2374, 2375, 2526, etc.

IPv6 Enhancements (1)

• Expanded address space– 128 bit

• Improved option mechanism– Separate optional headers between IPv6 header and

transport layer header– Most are not examined by intermediate routes

• Improved speed and simplified router processing• Easier to extend options

• Address autoconfiguration– Dynamic assignment of addresses

IPv6 Enhancements (2)

• Increased addressing flexibility– Anycast - delivered to one of a set of nodes– Improved scalability of multicast addresses

• Support for resource allocation– Replaces type of service– Labeling of packets to particular traffic flow– Allows special handling– e.g. real time video

Structure

Base Header

• Alignment has been changed from 32-bit to 64-bit multiples.

• The header length has been eliminated and the datagram length field has been replaced by a PAYLOAD LENGTH field.

• The size of source and destination address fields has been increased to 16 octets each.

Base Header (cont’d)

• Fragmentation information has been removed out of fixed fields into an extension header.

• The TIME-TO-LIVE field has been rep[laced by a HOP LIMIT field.

• The SERVICE TYPE is renamed to be a TRAFFIC CLASS field, and extended with a FLOW LABEL field.

• The PROTOCOL field has been replaced by the type of the next header.

Extension Headers

• Hop-by-Hop Options– Require processing at each router

• Routing– Similar to v4 source routing

• Fragment• Authentication• Encapsulating security payload• Destination options

– For destination node

Extension Headers (cont’d)

• IPv6 extension headers are similar to IPv4 options. Each datagram includes extension headers for only those facilities that the datagram uses.

IP v6 Header

IP v6 Header Fields (1)

• Version– 6

• Traffic Class– Classes or priorities of packet– Still under development– See RFC 2460

• Flow Label– Used by hosts requesting special handling

• Payload length– Includes all extension headers plus user data

IP v6 Header Fields (2)

• Next Header– Identifies type of header

• Extension or next layer up

• Source Address

• Destination address

IPv6 Base Header

From now on, they can’t call me

Junior!

Fragmentation Header

• Fragmentation only allowed at source

• No fragmentation at intermediate routers

• Node must perform path discovery to find smallest MTU of intermediate networks

• Source fragments to match MTU

• Otherwise limit to 1280 octets

Fragmentation Header Fields

• Next Header

• Reserved

• Fragmentation offset

• Reserved

• More flag

• Identification

End-to-End Fragmentation• An internet protocol that uses end-to-end fragmentation

requires a sender to discover the path MTU to each destination, and to fragment any outgoing datagram that is larger than the path MTU. End-to-end fragmentation does not accommodate route changes.

• To solve the problem of route changes that affect the path MTU, IPv6 includes a new ICMP error message. When a route discovers that fragmentation is needed, it sends the message back to the source. The source will fragment the datagrams based on the new minimum MTU.

Source Routing Header

• List of one or more intermediate nodes to be visited

• Next Header

• Header extension length

• Routing type

• Segments left– i.e. number of nodes still to be visited

IPv6 Options

Hop-by-Hop Options

• Next header• Header extension length• Options

– Jumbo payload• Over 216 = 65,535 octets

– Router alert• Tells the router that the contents of this packet is of

interest to the router• Provides support for RSPV (chapter 16)

Destination Options

• Same format as Hop-by-Hop options header

IPv6 Addresses

• 128 bits long

• Assigned to interface

• Single interface may have multiple unicast addresses

• Three types of address

Types of address

• Unicast– Single interface

• Anycast– Set of interfaces (typically different nodes)– Delivered to any one interface– the “nearest”

• Multicast– Set of interfaces– Delivered to all interfaces identified

Aggregatable Global Unicast Address Structure

Interface Identifier

Multicasting

• Addresses that refer to group of hosts on one or more networks

• Uses– Multimedia “broadcast”– Teleconferencing– Database– Distributed computing– Real time workgroups

Group Membership in IPv6

• Multicast addresses are used to define a group of hosts instead of one.

• All use the prefix 11111111 in the first field.• The second field is a flag that defines the group

address as either permanent or transient.• The third field is a SCOPE field which indicates

the scope to be node local(0001), link local (0010), site local(0101), organizational local (1000), or global(1110).

ICMP v6

• Function of IGMP included in ICMP v6

• New group membership termination message to allow host to leave group