Ch 18 intro to network layer - section 4

 IPV4 ADDRESSES
-Address Space.
-Hierarchy in addressing
-Classful Addressing.
-Classless Addressing.
-Dynamic Host Configuration Protocol(DHCP).

 The Internet address (IP address): the identifier used
to identify the connection of each device to the
Internet.
 The IP address may be changed if the device is moved
to another network.
 The IPv4 address: is a 32-bit address that uniquely and
universally defines the connection of a host to the
Internet.
 IPv4 addresses uniquely: Each address defines only
one connection to the Internet.
 IPv4 addresses universally: the addressing system must
be accepted by any host that wants to be connected
to the Internet.

 An address space is the total number of addresses
used by the protocol.
 If a protocol uses b bits to define an address, the
address space is 2^b.
 In binary notation, an IPv4 address is displayed as 32
bits.
 In hexadecimal notation, an IPv4 address is displayed
as 8 hexadecimal digits.
 Each octet is often referred to as a byte.

 A 32-bit IPv4 address is hierarchical, divided
into two parts.
 The first part of the address, called the
prefix, defines the network.
 the second part of the address, called the
suffix, defines the node.

 IPv4 address was designed with a fixed length
prefix.
 To accommodate both small and large networks,
three fixed-length prefixes were designed
instead of one (n = 8, n = 16, and n = 24).
 The whole address space was divided into five
classes (class A, B, C, D, and E).

 class A, network length is 8 bits, first bit 0, defines
the class, seven bits as the network identifier.
there are only 128 networks in the world that can
have a class A address.
 class B, network length is 16 bits, first two bits 10,
define the class,14 bits as the network identifier.
there are only 16,384 networks in the world that
can have a class B address.
 In class C, network length is 24 bits , three bits 110
define the class, 21 bits as the network identifier.
there are 2,097,152 networks in the world that can
have a class C address.

 Class A:can be assigned to only 128 organizations in the
world, but each organization needs to have a single
network with 16,777,216 nodes.
 Since there may be only a few organizations that are this
large, most of the addresses in this class were wasted
(unused).
 Class B addresses were designed for midsize organizations,
but many of the addresses in this class also remained
unused.
 Class C addresses have a completely different flaw in
design, The number of addresses that can be used in each
network (256 nodes) was so small that most companies
were not comfortable using a block in this address
 Class E addresses were almost never used, wasting the
whole class.

 In Subnetting, a class A or class B block is
divided into several subnets.
 Each subnet has a larger prefix length than the
original network.
 Supernetting was devised to combine several
class C blocks into a larger block to be
attractive to organizations that need more than
the 256 addresses available in a class C block.
 This idea did not work either because it makes
the routing of packets more difficult.

It had one advantage:
 Given an address, we can easily find the
class of the address and, since the prefix
length for each class is fixed, we can find the
prefix length immediately.
 In other words, the prefix length in classful
addressing is inherent in the address; no
extra information is needed to extract the
prefix and the suffix.

 In classless addressing, variable-length blocks are
used that belong to no classes.
 We can have a block of 1 address, 2 addresses, 4
addresses, 128 addresses, and so on.
 the whole address space is divided into variable
length blocks.
 The prefix defines the block (network);
 The suffix defines the node(device).

 the prefix length, n, is added to the address,
separated by a slash.
 The notation is informally referred to as slash
notation and formally as classless interdomain
routing (CIDR).

 1.The number of addresses in the block is
found as N = 2^(32−n);n is prefix.
 2.To find the first address, we keep the n
leftmost bits and set the (32 − n) rightmost
bits all to 0s.
 3.To find the last address, we keep the n
leftmost bits and set the (32 − n) rightmost
bits all to 1s.

The address mask is a 32-bit number in which
 The prefix bits are set to 1s.
 The rest of the bits are set to 0s.
1.The number of addresses in the block
N = NOT (mask) + 1.
2.The first address in the block =(Any address in
the block) AND (mask).
3.The last address in the block =(Any address in
the block) OR [(NOT (mask)].

 Network address, is particularly important
because it is used in routing a packet to its
destination network.
 Block Allocation: ICANN does not normally allocate
addresses to individual Internet users. It assigns a
large block of addresses to an ISP.
 The number of requested addresses, N, needs to
be a power of 2.
 The requested block needs to be allocated where
there is an adequate number of contiguous
addresses available in the address space.

 number of addresses is N
 the prefix length is n
 the assigned number of addresses to each
subnetwork is Nsub
 the prefix length for each subnetwork is nsub
 The number of addresses in each subnetwork
should be a power of 2.
 The prefix length for each subnetwork should be
found using the following formula:
 The starting address in each subnetwork should be
divisible by the number of addresses in that
subnetwork

 When blocks of addresses are combined to create
a larger block, routing can be done based on the
prefix of the larger block.
 ICANN assigns a large block of addresses to an
ISP. Each ISP in turn divides its assigned block
into smaller subblocks and grants the subblocks
to its customers.

 0.0.0.0/32 is called the host address.
 255.255.255.255/32 is called the limited-
broadcast address.
 127.0.0.0/8 is called the loopback address.
 private addresses: 10.0.0.0/8, 172.16.0.0/12,
192.168.0.0/16,and 169.254.0.0/16.
 224.0.0.0/4 is reserved for multicast addresses.

 DHCP is an application-layer program, using the client-
server paradigm, that actually helps TCP/IP at the network
layer.
 DHCP is a client-server protocol in which the client sends a
request message and the server returns a response
message.

 The technology allows a site to use a set of private addresses
for internal communication and a set of global Internet
addresses (at least one) for communication with the rest of the
world.
 The site must have only one connection to the global Internet
through a NAT-capable router that runs NAT software.

Ch 18 intro to network layer - section 4

Ch 18 intro to network layer - section 4

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Ch 18 intro to network layer - section 4