Notes On Chapter Twenty-Four -- The Future IP (IPv6)

• 24.1 Introduction
  
  
  • Future of the Internet Protocol
  • Strengths and Limitations of IPv4
  • Features of IPv6
  
  
• 24.2 The Success of IP
  
  
  • IPv4 has been quite successful - surviving considerable evolutionary change in hardware technology and network organization.
  
  
• 24.3 The Motivation for Change
  
  
  • The primary motivation for IPv6 is the perception that there are not enough 32-bit addresses to accommodate Internet growth.
  • Other desires:
    • Ways to assure low jitter for real-time audio and video (e.g. avoidance of route changes).
    • Anycast - e.g. connect me to the nearest server
    • Multicast and dynamic multicast group support
  
  
• 24.4 The Hourglass Model and Difficulty of Change
  
  
  • Refer to Figure 24.1 on page 407.
  • Although scarcity of addresses was considered a near-emergency in 1993 when work began on IPv6, the Internet is still mostly operating with IPv4.
  • If IP changes, much about the Internet will have to change with it.
  
  
• 24.5 A Name and a Version Number
  
  
  • IPv4 is the "old" IP
  • IPv6 is the "new" IP
  
  
• 24.6 IPv6 Features
  
  
  • Connectionless like IPv4
  • Has max hops field
  • Address Size is 128 bits
  • Header Format is quite different
  • Extension Headers: Datagram consists of base header, followed by zero or more extension headers, followed by data.
  • Support for Real-Time Traffic: IPv6 provides a mechanism for sender and receiver to establish a "high-quality" path and associate datagrams with that path.
  • Extensible Protocol
  
  
• 24.7 IPv6 Datagram Format
  
  
  • Refer to Figure 24.2 on page 409.
  
  
• 24.8 IPv6 Base Header Format
  
  
  • Refer to Figure 24.3 on page 410.
  • Refer to Figure 24.4 on page 411.
  • Most room in the base header is used for the source and destination addresses.
  • TRAFFIC CLASS field has to do with service requirements
  • NEXT HEADER field is used to implement the "linked list" of extension headers.
  
  
• 24.9 Implicit and Explicit Header Size
  
  
  • Refer to Figure 24.5 on page 411.
  
  
• 24.10 Fragmentation, Reassembly and Path MTU
  
  
  • Refer to Figure 24.6 on page 412.
  • There is a separate, special fragmentation header in fragments.
  • The unfragmentable part is the base header and headers that control routing.
  • The sending host is responsible to do the fragmenting.
  • A router will discard an IPv6 datagram that is too big to transmit, and send an error message to the sender.
  • A sender may calculate the path MTU by trial and error.
  
  
• 24.11 The Purpose of Multiple Headers
  
  
  • Datagrams can be smaller because unneeded headers are not included.
  • Smaller datagrams take less time to send.
  • A new feature can be added to the protocol without redefining the old headers.
  • Adding a new (or experimental) feature just means adding a new NEXT HEADER type and a new header format.
  
  
• 24.12 IPv6 Addressing
  
  
  • Refer to Figure 24.7 on page 415.
  • IPv6 addresses are hierarchical
  • Division between prefix and suffix 'floats' as with IPv4 CIDR.
  • IPv6 hierarchy can be multilevel - parts of the address to indicate ISP, organization, site, and so forth.
  • Addresses are unicast, multicast, or anycast.
  • The idea of anycast is to deliver to exactly one of the members of some group. This supports "replicated services."
  • Directed broadcast is 'gone' - it was a security problem to allow someone outside a network to send a packet to every host on the network - e.g. a ping.
  • Limited broadcast (from within) is implemented as multicast.
  
  
• 24.13 IPv6 Colon Hexadecimal Notation
  
  
  • To achieve some compactness, a colon hex form is used to write IPv6 addresses, e.g.

    
    	 69DC:8864:FFFF:FFFF:0:1280:8C0A:FFFF

    Above, each segment is a hexadecimal representation of a 16-bit section of the address.
  • Zero compression may be used - if there is a long run of zero's in the address, it can be replaced with a pair of colons.
  • Addresses are assigned to take advantage of zero compression. For example IPv4 addresses are mapped to all zero's, except for the last 32 bits.