Lecture 17: Network Layer: Logical addressing

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24 Οκτ 2013 (πριν από 3 χρόνια και 7 μήνες)

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NETWORK LAYER

Ch

19. Logical Addressing

19.1 IPv4 Addresses


For world
-
wide communications


Uniquely identify a device in the network


Logical address = IP address (in TCP/IP protocol)


IPv4 Address


32 bits long


2
32

address space


Globally unique


Notation (binary or dotted
-
decimal)

Classful

Addressing


Address space is divided into five classes: A, B, C, D, and E


netid

hostid

Classful

Addressing


Mask is used to find the
netid

and
hostid





Subnetting



divide a large block of addresses into
several groups (
increases the number of 1s in the mask
)


Supernetting



combine small blocks of addresses due
to depletion of class A and B addresses.


Address depletion


A large part of addresses were wasted

Classless Addressing


To overcome address depletion classless addressing is
used.


Allow a different size of address blocks with restrictions
of


Addresses in a block must be
contiguous


The number of addresses in a block is
a power of 2


The first address must be
divisible

by the number of
addresses

Classless Addressing


A block of addresses can be defined as


x.y.z.t /n


where x.y.z.t is
any address in the block


/
n defines
the mask


First n
bits are the
netid


The block can have up to 2
(32

n)

hosts



Practice with example 19.9


Exp
: 205.16.37.39/28 will be represented in binary as

11001101 00010000 00100101 0010
0111

(205.16.37.32 is the first address in the block)


The first address is often assigned to a special device, e.g., a gateway

Hierarchy of IPv4 Address


Comparison


Telephone number





IPv4 Address

Subnetting

(Multi
-
level Hierarchy)


“Internally” divide a block of addresses into
clusters of networks (called subnets)


An outside device still sees them as a single block

Example: Organization is given

17.12.14.0/26

00
0
00000

00
0
11111

00
10
0000

00
10
1111

00
11
0000

00
11
1111

17.12.14.

17.12.14.

17.12.14.

Needs to split in 3 groups.

Example 19.10


A block of addresses 190.100.0.0/16 needs to be distributed to three
groups as follows:


64 customers; each needs 256 addresses


128 customers; each needs 128 addresses


128 customers; each needs 64 addresses

Network Address Translation (NAT)


Addresses for private network


Home users have a small network, where each device
needs an IP address


Some addresses are reserved for “internal network”





Anyone can use these addresses without permission

NAT


The private network should has one single
connection to the Internet





Address translation

Translation Table

Translation Table


Entry of a table may …


use one (global) IP address


use a pool of (global) IP addresses


often used by
ISP (see below)


use both IP address and port number


often
known as IP sharing


NAT and ISP

19.2 IPv6 Addresses


IPv6
Address


128
bits long


2
128

address space


Globally
unique


Notation (hexadecimal colon)



Abbreviated representation

Address Structure


Unicast





Multicast

Homework


Exercise


18


19


22


26