Kingdom of Saudi Arabia
Prince Norah bint Abdul Rahman University
College of Computer Since and Information System
NET331
NETWORK LAYER (2)
T.Najah AlSubaie
1
IP Address
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The communication at the network layer is host-to-host
(Source-to-destination);
The packet transmitted by the sending computer may
pass through several LANs or WANs before reaching
the destination computer.
For this level of communication, we need a global
addressing scheme; we called this logical addressing in
Chapter 2
We use the term IP address to mean a logical address
in the network layer of the TCP/IP protocol suite
IP Address
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The Internet addresses are 32 bits in length.
This gives us a maximum of 232 addresses.
These addresses are referred to as IP addresses.
An IP address is uniquely and universally defines
the connection of a device (for example, a computer
or a router) to the Internet.
Two devices on the Internet can never have the
same address at the same time
Address Space
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An address space is the total number of addresses
used by the protocol.
If a protocol uses N bits to define an address, the
address space is 2N because each bit can have two
different values (0 or 1) and N bits can have 2N
values.
Notations
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There are two prevalent notations to show an IP
address: binary notation and dotted-decimal
notation.
Binary Notation
In binary notation, the IP address is displayed as 32
bits.
 Each octet is often referred to as a byte.
 So it is common to hear an IP address referred to as
a 32-bit address or a 4-byte address.
 The following is an example of an IP address in
binary notation:
01110101 10010101 00011101 00000010
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Dotted-Decimal Notation
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To make the IP address more compact and easier to
read, Internet addresses are usually written in
decimal form with a decimal point (dot) separating
the bytes.
The following is the dotted-decimal notation of the
address (01110101 10010101 00011101 00000010)
117.149.29.2
dotted-decimal notation and binary
notation for an IPv4 address
Example
Change the following IP addresses from binary notation
to dotted-decimal notation.
a.
10000001 00001011 00001011 11101111
b.
11000001 10000011 00011011 11111111
Solution
We replace each group of 8 bits with its equivalent
decimal number (see Appendix B) and add dots for
separation.
a.
129.11.11.239
b.
193.131.27.255
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Example
Change the following IPv4 addresses from dotteddecimal notation to binary notation.
a. 111.56.45.78
b. 221.34.7.82
Solution
We replace each decimal number with its binary
equivalent .
a. 01101111 00111000 00101101 01001110
b. 11011101 00100010 00000111 01010010
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Example
Find the error, if any, in the following IPv4 addresses.
a. 111.56.045.78
b. 221.34.7.8.20
c. 75.45.301.14
d. 11100010.23.14.67
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Solution
a. There must be no leading zero (045).
b. There can be no more than four numbers in an IPv4 address.
c. Each number needs to be less than or equal to 255 (301 is outside
this range).
d. A mixture of binary notation and dotted-decimal notation is not
allowed.
Routing
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Routing means to place the packet in its route to its
destination.
Routing requires a host or a router to have a routing
table. When a host has a packet to send or when a
router has received a packet to be forwarded, it
looks at this table to find the route to the final
destination
Routing
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A dynamic table, is one that is updated
automatically when there is a change somewhere in
the internet.
For instance, they need to be updated when a
router is down, and they need to be updated
whenever a better route has been found.
Optimization
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Router is usually attached to several networks.
When it receives a packet, the decision of what
network should it pass the packet is based on the
optimization criteria.
Optimization
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Optimality can be defined by several approaches :
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A cost is assigned for passing through a network. We call this
cost a metric.
One protocol, allow the administrator to assign a cost for passing
through a network based on the type of service required.
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if maximum throughput is the desired type of service, a satellite link
has a lower metric than a fiber-optic line.
On the other hand, if minimum delay is the desired type of service, a
fiber-optic line has a lower metric than a satellite link.
Other protocol treat all network as equals. It is one hop count.
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If packet passes through networks to reach the destination. The total
cost is 10 hope counts.
Routing Protocols
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Routing protocols have been created in response to
the demand for dynamic routing tables.
A routing protocol is a combination of rules and
procedures that lets routers in the internet inform
each other of changes.
Routing
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Intra and Inter-domain Routing
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An autonomous system (AS) is a group of networks
and routers under the authority of a single
administration.
Routing inside an autonomous system is referred to
as intradomain routing.
Routing between autonomous systems is referred to
as interdomain routing.
Distance vector routing tables
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In distance vector routing, each node shares its routing
table with its immediate neighbors periodically and
when there is a change.
In distance vector routing, the least-cost route between
any two nodes is the route with minimum distance.
In this protocol, each node maintains a vector (table) of
minimum distances to every node.
The table at each node also guides the packets to the
desired node by showing the next stop in the route
(next-hop routing).
Distance vector routing tables
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Initialization of tables in distance
vector routing
Updating in distance vector routing
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Two node insatiability
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Link State Routing
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In link state routing, if each node in the domain has
the entire topology of the domain, the list of nodes
and links.
The node can use Dijkstra's algorithm to build a
routing table.
Each node uses the same topology to create a
routing table.
Concept of link state routing
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Link state knowledge
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Example of formation of shortest path
tree
Routing table for node A
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Path Vector Routing
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Path vector routing proved to be useful for
interdomain routing.
we assume that there is one node in each
autonomous system that acts on behalf of the entire
autonomous system. This nod is called a speaker
node.
Only speaker nodes in each AS can communicate
with each other.
A speaker node advertises the path, not the metric
of the nodes
Path Vector Routing
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Path vector includes tow phases:
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Initialization:
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Sharing:
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Each speaker node can know only the reachability of nodes
inside its autonomous system.
A speaker in an autonomous system shares its table with
immediate neighbors.
Updating
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When a speaker node receives a two-column table from a
neighbor, it updates its own table by:
adding the nodes that are not in its routing table
 adding its own autonomous system and the autonomous
system that sent the table
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Initial routing tables in path vector
routing
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Stabilized tables for three autonomous
systems
Multicasting and Broadcasting
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In multicast communication, there is one source and
a group of destinations.
The relationship is one-to-many.
In this type of communication, the source address is
a unicast address, but the destination address is a
group address, which defines one or more
destinations.
Broadcasting
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In broadcast communication, the relationship
between the source and the destination is one-to-all.
There is only one source, but all the other hosts are
the destinations.