Chapter 2 The Architecture of Networks

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Chapter 2 The Architecture of Networks
Organizing with Layers and Architectures
How does a computer network work?
If you do not understand the basics, please
read Andrew Tanenbaums Computer Networks.
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Chapter 2 The Architecture of Networks
Organizing with Layers and Architectures
3
Chapter 2 The Architecture of Networks
Organizing with Layers and Architectures
???? (Peer Protocol)
?N?
?N-1?
?1?
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Chapter 2 The Architecture of Networks
Organizing with Layers and Architectures
Encapsulation and Decapsulation
FTP
TCP
IP
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Chapter 2 The Architecture of Networks
Organizing with Layers and Architectures
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Chapter 2 The Architecture of Networks
Organizing with Layers and Architectures
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
What about disadvantages?
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Chapter 2 The Architecture of Networks
Organizing with Layers and Architectures
application
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ISO OSI?????
presentation
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session
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transport
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network
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data link
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physical
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Chapter 2 The Architecture of Networks
The TCP/IP Internet TCP/IP Protocols
TCP/IP Layering
(define or reference over 1000 distinct
communication protocols)
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Chapter 2 The Architecture of Networks
The TCP/IP Internet Links, Subnetworks, and
Internets
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Chapter 2 The Architecture of Networks
The TCP/IP Internet Hosts and Routers
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Chapter 2 The Architecture of Networks
The TCP/IP Internet Hosts and Routers
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Chapter 2 The Architecture of Networks
The TCP/IP Internet Internet Hierarchy
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Chapter 2 The Architecture of Networks
Communication Services Connectionless Delivery
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Chapter 2 The Architecture of Networks
Communication Services Connectionless Delivery
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Chapter 2 The Architecture of Networks
Communication Services Connection-Oriented
Delivery
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Chapter 2 The Architecture of Networks
Communication Services Connection-Oriented
Delivery
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Chapter 2 The Architecture of Networks
Communication Services Combining Services
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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.
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.
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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.
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Chapter 2 The Architecture of Networks
Network Addressing Type of Addresses Unicast,
Muticast, Anycast
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Chapter 2 The Architecture of Networks
Network Addressing Type of Addresses Unicast,
Muticast, Anycast
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Chapter 2 The Architecture of Networks
Network Addressing IPv4 address format (32-bit
address)
class A
0
7-bit netid
24-bit hostid
class B
1 0
16-bit hostid
14-bit netid
??? 26
class C
1 1 0
8-bit hostid
21-bit netid
class D
1 1 1 0
28-bit multicast group ID
class E
1 1 1 1 0
reserved for future use
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.
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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.
Changing network addresses can be incredible
time-consuming and difficult to debug.
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Chapter 2 The Architecture of Networks
Network Addressing IPv4 address format (32-bit
address)
Typical Routing Table Format
Destination-Network Next Hop Mask
100.203.10.x 100.204.10.1
255.255.255.0
Router
Router
100.204.10.1
100.203.10.1
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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
Supernetting Classless Inter Domain Routing
(CIDR) Assign class C in chunks of power of 2.
For example, Assign 203.64.0. 203.64.3. to
one organization. Then we can have a mask of
255.255.252.0.
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Chapter 2 The Architecture of Networks
Network Addressing IPv4 address format (32-bit
address)
IPv4 address weakness
Another problem
The usual A to B path
Network 1
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.
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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 xxxxxxxx, where the 'x's
are the hexadecimal values of the eight
16-bit pieces of the address. Examples
FEDCBA9876543210FEDCBA98765
43210 10800008800200C41
7A
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Chapter 2 The Architecture of Networks
Network Addressing IPv6 address format (128-bit
address)
Text Representation of Addresses
Note that it is not necessary to write
the leading zeros in an individual field,
but there must be at least one numeral in
every field (except for the case described in
2.).
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.
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Chapter 2 The Architecture of Networks
Network Addressing IPv6 address format (128-bit
address)
Text Representation of Addresses
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.
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Chapter 2 The Architecture of Networks
Network Addressing IPv6 address format (128-bit
address)
Text Representation of Addresses
For example the following addresses 10800008
800200C417A 10808800200c417A
FF0100000043
FF0143 00000001
1 (Loopback address)
00000000
(unspecified address)
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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
xxxxxxd.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, 00000013.1.68.3 in compressed
form is 13.1.68.3
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Chapter 2 The Architecture of Networks
Network Addressing IPv6 address format (128-bit
address)
Hierarchy
35161683280
The remaining 48 bits define the particular
system on the subnetwork.
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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.
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Chapter 2 The Architecture of Networks
Network Addressing IPv6 address format (128-bit
address)
IPv6 Address Allocation
Allocation
Prefix Fraction of
(binary)
Address Space -------------------------------
-------- ------------- Reserved
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)
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Chapter 2 The Architecture of Networks
Network Addressing IPv6 address format (128-bit
address)
IPv6 Address Allocation
Allocation
Prefix Fraction of
(binary)
Address Space -------------------------------
-------- ------------- Aggregatabl
e Global Unicast Addresses
001 1/8
(20003) 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)
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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)
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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 IPv6 Addresses The IPv6
transition mechanisms include a technique for
hosts and routers to dynamically tunnel IPv6
packets over IPv4 routing infrastructure.
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
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Chapter 2 The Architecture of Networks
Network Addressing IPv6 address format (128-bit
address)
IPv4-compatible IPv6 Addresses
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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.
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Chapter 2 The Architecture of Networks
Network Addressing IPv6 address format (128-bit
address)
IPv4-mapped IPv6 address
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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. Either address format contributes the same
value to the checksum, whether it is specified as
an IPv6 addresses or as an IPv4 address.
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Chapter 2 The Architecture of Networks
Network Addressing IPv6 address format (128-bit
address)
Anycast Address (the subnet-router address)
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Chapter 2 The Architecture of Networks
Network Addressing IPv6 address format (128-bit
address)
Multicast Address
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Chapter 2 The Architecture of Networks
Network Addressing IPv6 address format (128-bit
address)
Multicast Address
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Chapter 2 The Architecture of Networks
Network Addressing IPv6 address format (128-bit
address)
Multicast Address
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Chapter 2 The Architecture of Networks
Network Addressing IPv6 address format (128-bit
address)
Multicast Address
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Chapter 2 The Architecture of Networks
Network Addressing IPv6 address format (128-bit
address)
Multicast Address
Assigned Multicast Addresses
FF011 all systems
node-local scope FF021 all
systems link-local scope FF012
all routers node-local
scope FF022 all routers
link-local scope FF052 all
routers site-local scope
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Chapter 2 The Architecture of Networks
Network Addressing IPv6 address format (128-bit
address)
Solicited node 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
FE021FF00/104. For example, a host with
unicast address FEDCBA9876543210FEDCBA987654
3210 automatically belongs to the group of
systems with multicast address FE021FF543210.
ICMP uses solicited node addresses to perform
neighbor discovery and duplicate address
detection.
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Chapter 2 The Architecture of Networks
Network Addressing IPv6 address format (128-bit
address)
Addresses that host must support
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Chapter 2 The Architecture of Networks
Network Addressing IPv6 address format (128-bit
address)
Addresses that router must support