Docstoc

ch2

Document Sample
ch2 Powered By Docstoc
					Chapter 2 The Architecture of Networks
 Organizing with Layers and Hierarchies
   •Layers organize effort-divide and conquer




                                                1
Chapter 2 The Architecture of Networks
 Organizing with Layers and Hierarchies
                                          對等協定
第N層                                       (Peer Protocol)



第N-1層




第1層
                      傳輸介質


                                                        2
Chapter 2 The Architecture of Networks
 Organizing with Layers and Hierarchies

        FTP                 Encapsulation and
                            Decapsulation

      TCP

 IP




                                                3
Chapter 2 The Architecture of Networks
 Organizing with Layers and Hierarchies
    •Hierarchies organize information and delegate responsibility




                                                                    4
Chapter 2 The Architecture of Networks
 Organizing with Layers and Hierarchies

 Layering Advantages :
    •Isolating the various services from one another
    •Flexibility (changing from cable to fiber without your knowing)


 Hierarchies Advantages:
    •Organize information and delegate responsibility




                                                                  5
 Chapter 2 The Architecture of Networks
   Layers
       •different communication protocols
   Hierarchies
       Internet naturally organizes its components into hierarchies

            應用層             application        應用層
            表達層             presentation       表達層
ISO                          session
            交談層                                交談層
OSI的
參考模         傳輸層              transport         傳輸層
型                            network
            網路層                                網路層
          資料連結層             data link         資料連結層
            實體層             physical           實體層
                            傳輸介質
                                                                      6
Chapter 2 The Architecture of Networks
  Two distinct roles for Internet
     •Host and Router
  The TCP/IP Internet: TCP/IP Protocols
                          TCP/IP Layering




                                            7
Chapter 2 The Architecture of Networks
 The TCP/IP Internet: Links, Subnetworks, and Internets




Network: has a completely routing ability
Internet: join several network (herein define subnetwork) together   8
Chapter 2 The Architecture of Networks
  The TCP/IP Internet:
     •Hosts: send or receive messages
     •Routers: relay messages across networks




                                                9
Chapter 2 The Architecture of Networks
The TCP/IP Internet: Hosts and Routers (protocol stacks)




                                                           10
Chapter 2 The Architecture of Networks
  The TCP/IP Internet: Internet Hierarchy




 Site: collection of networks, controlled by a single administrator
                                                                      11
Chapter 2 The Architecture of Networks
  Communication Services: Connectionless Delivery




                                                    12
Chapter 2 The Architecture of Networks
  Communication Services: Connectionless Delivery




                                                    13
Chapter 2 The Architecture of Networks
  Communication Services: Connection-Oriented Delivery




                                                    14
Chapter 2 The Architecture of Networks
  Communication Services: Connection-Oriented Delivery




                                                    15
Chapter 2 The Architecture of Networks
  Communication Services: Combining Services




                   (TCP, CO)
                     (IP, CL)

       (TCP, CO)




                                               16
Chapter 2 The Architecture of Networks
 Network Addressing

   Internet Protocol software must hide the details of physical
   networks and offer the facilities of a large virtual network
   (hide the differential network technology).

   The Internet designers are free to choose addresses, packet
   formats, and delivery techniques independent of the details
   of the physical hardware.

   Addressing is a critical component of the Internet abstract.
   To give the appearance of a single, uniform system, all host
   computers must use a uniform addressing scheme.


                                                                  17
Chapter 2 The Architecture of Networks
 Network Addressing: The role of network addresses
  IP addresses do not specify an individual computer, but
  a connection to a network.
  TCP/IP addresses identify interfaces, not systems
  Multi-home host: more than one network interface, each interface
                    requires one network address




                                                               18
Chapter 2 The Architecture of Networks
 Network Addressing: Type of Addresses
    •Unicast, Muticast, Anycast




                                         19
Chapter 2 The Architecture of Networks
Network Addressing: Type of Addresses
Unicast, Muticast, Anycast (compromise between unicast and multicast)




 Anycast address refers to any one of interfaces, not all of them
 Ex: router recognizes that the message has already reached at least one
 appropriate interface                                                     20
Network Addressing: IPv4 address format (32-bit address)
 IP denoted - in the form <a.b.c.d> each number represents,
  in decimal, 1 byte of the 4-byte IP address.
 Why are IP addresses necessary?
      Easy to find the destination station
      IP addresses are hierarchical addresses
        • Every IP address has two parts.
            – network number (provided by InterNIC)
            – host number (provided by local administrator)
      Where to find the IP address
        • International Network Information Center, or InterNIC
      There are five classes of Network (Five type IP)
        • only three of these are used commercially. These are the class "A," "B,"
          and "C" networks
        • the class “D” is reserved for multicast
        • the class “E” is reserved for experiment/research
                                                                                     21
Chapter 2 The Architecture of Networks
   Network Addressing: IPv4 address format (32-bit address)

 class A   0 7-bit netid          24-bit hostid                     0 ~ 127

 class B   1 0 14-bit netid                16-bit hostid            128 ~ 191
 class C   110          投影片
                    21-bit netid 26                  8-bit hostid   192 ~ 223
 class D   1110            28-bit multicast group ID                224 ~ 239
 class E   11110           reserved for future use                   240 ~ 255

   Note that the IP address has been defined in such a way that
   it is possible to extract the hostid or netid portions quickly.
   Routers, which use the netid portion when deciding where to
   send a packet, depend on efficient extraction to achieve high
   speed.
                                                                                 22
 What IP addresses are reserved for the Networks?
      Network address : all host address are set to zero
      Broadcase address : all host address are set to one
 Question: What would the network/broadcase address be
  for devices such as the one with an IP address of
  197.22.103.221?
 In order to provide extra flexibility for the network
  administrator, often networks, particularly large networks,
  are divided into smaller networks called subnetworks.
  Most of the time subnetworks are simply referred to as
  subnets.
 Who assigns subnet addresses?
      this is done by the network administrator

                                                             23
Chapter 2 The Architecture of Networks
  Network Addressing: IPv4 address format (32-bit address)
  IPv4 address weakness:

  The most obvious disadvantage is that addresses refer to
  network connections, not to host computer:
  If a host computer moves from one network to another,
  its IP address must change.
  Inconvenient for mobile computers

  Another weakness:
  Class C is too small while class B is too large.




                                                             24
Chapter 2 The Architecture of Networks
  Network Addressing: IPv4 address format (32-bit address)
 What is NetMask?


 Typical Routing Table Format (Router A)
    Destination-Network Next Hop             Mask
    100.203.10.x       100.204.10.1       255.255.255.0




                  100.204.10.1              100.203.10.1
      Router A                   Router



                                                             25
Chapter 2 The Architecture of Networks
  Network Addressing: IPv4 address format (32-bit address)

 Network Mask
 Subnetting: Subdivide the host-id field in IP address
   divide class C into subnets of power of 2
   for example:
      assign 192.100.100.0~63, 64~127, 128~191, 192~255 to
      four subnets. We can have a mask of 255.255.255.192

 Supernetting: Assign class C in chunks of power of 2 (supernet).
  For example,
   Assign 203.64.0.* ~ 203.64.3.* to one organization. Then
   we can have a mask of 255.255.252.0.

  Classless Inter Domain Routing (CIDR)
                                                                    26
Chapter 2 The Architecture of Networks
  Network Addressing: IPv4 address format (32-bit address)
  IPv4 address weakness:
  Another problem:

                     Network 1        The usual A to B path

                                                    I
        R                   A                   B


                     Network 2
   When link I fails, we have one address that can be used to
   reach B and another that can't. Routing table only records
   one path. It may take a long time to find out the other path.
                                                                   27
Chapter 2 The Architecture of Networks
  Network Addressing: IPv6 address format (128-bit address)

 Text Representation of Addresses

  There are three conventional forms for representing IPv6
  addresses as text strings:

   1. The preferred form is x:x:x:x:x:x:x:x, where the 'x's are the
     hexadecimal values of the eight 16-bit pieces of the address.
     Examples:
            FEDC:BA98:7654:3210:FEDC:BA98:7654:3210
            1080:0:0:0:8:800:200C:417A



                                                                      28
Chapter 2 The Architecture of Networks
  Network Addressing: IPv6 address format (128-bit address)
  Text Representation of Addresses
  2. Due to the method of allocating certain styles of IPv6
       addresses, it will be common for addresses to contain long
       strings of zero bits.
       In order to make writing addresses containing zero bits
       easier a special syntax is available to compress the zeros.
       The use of "::" indicates multiple groups
       of 16-bits of zeros. The "::" can only appear once in an
       address. The "::" can also be used to compress the leading
       and/or trailing zeros in an address.




                                                                     29
Chapter 2 The Architecture of Networks
  Network Addressing: IPv6 address format (128-bit address)

 Text Representation of Addresses

   For example the following addresses:

   1080:0:0:0:8:800:200C:417A             1080::8:800:200c:417A
   FF01:0:0:0:0:0:0:43                     FF01::43
   0:0:0:0:0:0:0:1                         ::1 (Loopback address)
   0:0:0:0:0:0:0:0                         :: (unspecified address)




                                                                      30
Chapter 2 The Architecture of Networks
  Network Addressing: IPv6 address format (128-bit address)

 Text Representation of Addresses

 3. An alternative form that is sometimes more convenient when
    dealing with a mixed environment of IPv4 and IPv6 nodes is
    x:x:x:x:x:x:d.d.d.d, where the 'x's are the hexadecimal values
    of the six high-order 16-bit pieces of the address, and the 'd's
    are the decimal values of the four low-order 8-bit pieces of the
    address (standard IPv4 representation).
    For example, 0:0:0:0:0:0:13.1.68.3 in compressed form
                 is ::13.1.68.3



                                                                       31
Chapter 2 The Architecture of Networks
    Network Addressing: IPv6 address format (128-bit address)
    Hierarchy: solve the routing table explosion
        •Different level only lookup the associated level information




3+5+16+16+8+32=80
The remaining 48 bits define the particular system on the subnetwork.
                                                                        32
Chapter 2 The Architecture of Networks
  Network Addressing: IPv6 address format (128-bit address)
  Address Prefixes

    An address prefix indicates both an address itself, and the
    number of significant bits in the addresses.




                                                                  33
Chapter 2 The Architecture of Networks
  Network Addressing: IPv6 address format (128-bit address)
  IPv6 Address Allocation – Special Addresses


  Allocation                       Prefix    Fraction of
                                   (binary)  Address Space
  -------------------------------   -------- -------------
  Reserved hierarchy              0000 0000 1/256 (0::/8)
  Unassigned                      0000 0001    1/256 (100::/8)
  Reserved for NSAP Allocation 0000 001        1/128 (200::/7)
  Reserved for IPX Allocation     0000 010     1/128 (400::/7)
  Unassigned                      0000 011     1/128 (600::/7)
  Unassigned                      0000 1       1/32 (800::/5)
  Unassigned                      0001         1/16 (1000:/4)

                                                                 34
Chapter 2 The Architecture of Networks
  Network Addressing: IPv6 address format (128-bit address)
   IPv6 Address Allocation
 Allocation                         Prefix      Fraction of
                                   (binary)     Address Space
 -------------------------------     --------   -------------
 Aggregatable Global Unicast
     Addresses                       001        1/8 (2000::/3)
 Unassigned                          010        1/8 (4000::/3)
 Unassigned                          011        1/8 (6000::/3)
 Unassigned                          100        1/8 (8000::/3)
 Unassigned                          101        1/8 (A000::/3)
 Unassigned                          110        1/8 (C000::/3)
 Unassigned                          1110       1/16 (E000::/4)

                                                                  35
Chapter 2 The Architecture of Networks
  Network Addressing: IPv6 address format (128-bit address)
  IPv6 Address Allocation

  Allocation                        Prefix        Fraction of
                                   (binary)      Address Space
  ------------------------------- --------       -------------
  Unassigned                      1111 0           1/32 (F000::/5)
  Unassigned                      1111 10          1/64 (F800::/6)
  Unassigned                      1111 110         1/128 (FC00::/7)
  Unassigned                      1111 1110 0     1/512 (FE00::/9)
  Link Local Unicast Addresses 1111 1110 10       1/1024 (FE80::/10)
  Site Local Unicast Addresses    1111 1110 11    1/1024 (FEC0::/10)
  Multicast Addresses             1111 1111        1/256 (FF00::/8)


                                                                       36
Chapter 2 The Architecture of Networks
  Network Addressing: IPv6 address format (128-bit address)
  IPv6 Address Allocation – Special Addresses
      0:0:0:0:0:0:0:0 unspecified address (never appear in the destination field)
      0:0:0:0:0:0:0:1 loopback address




                                                                                37
Chapter 2 The Architecture of Networks
   Network Addressing: IPv6 address format (128-bit address)
   Two types of IPv6 addresses support the transition from IPv4.
     IPv4-compatible and IPv4-mapped

IPv4-compatible IPv6 Addresses

The IPv6 transition mechanisms include a technique for hosts and
  routers to dynamically tunnel IPv6 packets over IPv4 routing
  infrastructure. Router at the boundary of the IPv4 network can
convert those address to true IPv4 addresses
IPv6 nodes that utilize this technique are assigned
  special IPv6 unicast addresses that carry an IPv4 address in the
  low-order 32-bits. This type of address is termed an "IPv4-
  compatible IPv6 address" and has the format:
                      96 bits
   |0000..............................00000000| IPv4 address |
                                                                     38
Chapter 2 The Architecture of Networks
  Network Addressing: IPv6 address format (128-bit address)

  IPv4-compatible IPv6 Addresses




                                                              39
Chapter 2 The Architecture of Networks
  Network Addressing: IPv6 address format (128-bit address)


 IPv4-mapped IPv6 address

  IPv4-mapped addresses indicate systems that do not support
  IPv6. They are instead limited to IPv4. As long as intervening
  routers perform the mapping, these addresses let IPv6 systems
  communicate with IPv4-only systems

  The format is 80 bits of zero, 16 bits of one, and 32 bits of an
  IPv4 address.
  Ex: IPv4: 4.3.2.1 , IPv4-mapped: ::FFFF:0403:0201



                                                                     40
Chapter 2 The Architecture of Networks
  Network Addressing: IPv6 address format (128-bit address)

 IPv4-mapped IPv6 address




                                                              41
Chapter 2 The Architecture of Networks
  Network Addressing: IPv6 address format (128-bit address)


  The structure of both IPv4-compatible and IPv4-mapped
  addresses is not arbitrary. Both formats were chosen
  because of the particular checksum algorithm that many
  TCP/IP protocols use. (for pseudo header)

  Either address format contributes the same value to the
  checksum, whether it is specified as an IPv6 addresses or as
  an IPv4 address.




                                                                 42
Chapter 2 The Architecture of Networks
  Network Addressing: IPv6 address format (128-bit address)
   Anycast Address (the subnet-router address)




                                                              43
Chapter 2 The Architecture of Networks
  Network Addressing: IPv6 address format (128-bit address)

Multicast Address: begin with eight bits of 1, the next eight bits
                    give more information about the address
                   (so far, only the fourth bit ha a defined meaning)




T=0: a global authority has permanently assigned the address
    to a particular group. Ex: FF02::1 identifies the group of all systems on a link
                                                                                   44
Chapter 2 The Architecture of Networks
  Network Addressing: IPv6 address format (128-bit address)

   Multicast Address




                                                              45
Chapter 2 The Architecture of Networks
  Network Addressing: IPv6 address format (128-bit address)

   Multicast Address




                                                              46
Chapter 2 The Architecture of Networks
  Network Addressing: IPv6 address format (128-bit address)

   Multicast Address




                                                              47
Chapter 2 The Architecture of Networks
  Network Addressing: IPv6 address format (128-bit address)

   Multicast Address
     Standard identified five permanently assigned address

       FF01::1         all systems         node-local scope
       FF02::1         all systems         link-local scope
       FF01::2         all routers         node-local scope
       FF02::2         all routers         link-local scope
       FF05::2         all routers         site-local scope




                                                              48
Chapter 2 The Architecture of Networks
  Network Addressing: IPv6 address format (128-bit address)
    Solicited node address (one of multicast address)
 Every unicast (or anycast) address maps to exactly one solicited
 node address. Different unicast addresses may form the same
 solicited node address.
 TO create a solicited node address, a system takes the last
 24-bits of its unicast or anycast address and appends them
 to the 104-bit prefix FE02::1:FF00/104. For example, a
 host with unicast address
 FEDC:BA98:7654:3210:FEDC:BA98:7654:3210 automatically
 belongs to the group of systems with multicast address
 FE02::1:FF54:3210.
 ICMP uses solicited node addresses to perform neighbor
 discovery and duplicate address detection.
                                                                    49
Chapter 2 The Architecture of Networks
  Network Addressing: IPv6 address format (128-bit address)

    Addresses that host must support




                                                              50
Chapter 2 The Architecture of Networks
  Network Addressing: IPv6 address format (128-bit address)

    Addresses that router must support




                                                              51

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:2
posted:9/10/2011
language:English
pages:51