Computer networks for cse Unit-3 (1).pptx

UNIT III-NETWORK LAYER
1
Contents
•Network Layer Design issues
• store and forward packet switching
•connection less and connection
oriented networks
•Routing algorithms
optimality principle
 shortest path
Flooding
Distance Vector Routing
Count to Infinity Problem
Link State Routing
 Path Vector Routing
Hierarchical Routing
Congestion control algorithms
•IP Addresses
•CIDR
•SubNetting
•SuperNetting
•IPv4
•Packet Fragmentation
•IPv6 protocol
•Transition from IPv4 to
IPv6
•ARP
•RARP

Network Layer
Network layer works for the transmission of data from one
host to the other located in different networks.
The functions of the Network layer are :
1.Routing: The network layer protocols determine which
route
is suitable from source to destination.
1.Logical Addressing: The sender & receiver’s IP address are
placed in the header by network layer. Such an address
distinguishes each device uniquely and universally.
* Segment in Network layer is referred as Packet.

What is packet?
• All data sent over the Internet is broken down into smaller
chunks called "packets.“
• A packet has two parts: the header, which contains senders and
receivers IP address, and the body, which is the actual data
being sent.
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Network Layer Design Issues:
1. Store-and-Forward Packet Switching
2. Services Provided to the Transport Layer
3. Implementation of Connectionless Service
4. Implementation of Connection-Oriented Service
5. Comparison of Virtual-Circuit and Datagram
Subnets

1. Store-and-Forward Packet Switching:
• The node which has a packet to send, delivers it to the nearest
router. The packet is stored in the router until it has fully arrived
and its checksum is verified for error detection.
• Once, this is done, the packet is forwarded to the next router.
Since, each router needs to store the entire packet before it can
forward it to the next hop, the mechanism is called store − and −
forward switching.
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Network layer protocol environment

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2. Services Provided to the Transport Layer
The network layer provides services to the transport layer at the
network layer/transport layer interface. The network layer services
have been designed with the following goals:
1. The services should be independent of the router technology.
2. The transport layer should be shielded from the number, type,
and topology of the routers present.
3. The network addresses made available to the transport layer
should use a uniform numbering plan, even across LANs and
WANs.
The network layer should provide connection-oriented service or
connectionless service

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3.Implementation of Connectionless Service
• If connectionless service is offered, packets are injected into the
subnet individually and routed independently of each other.
• In this context, the packets are frequently called datagram’s and
the subnet is called a datagram subnet.
• If connection-oriented service is used, a path from the source
router to the destination router must be established before any
data packets can be sent. This connection is called a VC (virtual
circuit) and the subnet is called a virtual-circuit subnet.

Routing within a diagram
subnet. 8

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4. Implementation of Connection-Oriented Service
• For connection-oriented service, we need a virtual-circuit
subnet.
• The idea behind virtual circuits is to avoid having to choose
a new route for every packet sent.
• when a connection is established, a route from the source
machine to the destination machine is chosen as part of the
connection setup and stored in tables inside the routers.
• When the connection is released, the virtual circuit is also
terminated. With connection-oriented service, each packet
carries an identifier telling which virtual circuit it belongs to.

Routing within a virtual-circuit subnet

5. Comparison of Virtual-Circuit and Datagram Subnets
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Routing
Algorithms
The main function of the network layer is routing packets from
the source machine to the destination machine.
There are two processes inside router:
a)One of them handles each packet as it arrives, looking up the
outgoing line to use for it in the routing table. This process is
forwarding.
b)The other process is responsible for filling in and updating
the routing tables. That is where the routing algorithm comes
into play. This process is routing.
Regardless of whether routes are chosen independently for each
packet or only when new connections are established, certain
properties are desirable in a routing algorithm correctness,
simplicity, robustness, stability, fairness, optimality

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Routing algorithms can be grouped into two major classes:
1. Non-Adaptive Algorithms –
These are the algorithms which do not change their
routing decisions once they have been selected. This is also
known as static routing as route to be taken is computed in
advance and downloaded to routers when router is booted.
2. Adaptive Algorithms -
These are the algorithms which change their routing
decisions whenever network topology or traffic load changes.
The changes in routing decisions are reflected in the topology
as well as traffic of the network.

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• Optimality principle
• Shortest path algorithm
• Flooding
• Distance vector routing
• Link state routing
• Path vector routing
• Hierarchical Routing
• Congestion control algorithms
Different Routing Algorithms

1. The Optimality Principle :
Statement of the optimality principle :
It states that if the router J is on the optimal path from router I to
router K, then the optimal path from J to K also falls along the
same route.
Call the route from I to J r1 and the rest of the route r2(J to K). it
could be concatenated with r1 to improve the route from I to K,
contradicting our statement that r1r2 is optimal only if a route
better than r2 existed from J to K.
Sink Tree for routers :
We can see that the set of optimal routes from all sources to a
given destination from a tree rooted at the destination as a
directed consequence of the optimality principle. This tree is
called a sink tree and is illustrated in fig(1).

Description of figure :
In the given figure the distance metric is the number of hops. Therefore, the goal of all
routing algorithms is to discover and use the sink trees for all routers.

Computer networks for cse Unit-3 (1).pptx

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2. Shortest Path Routing
• In shortest path routing, the topology
communications
network is represented using a directed weighted graph.
• The nodes in the graph represent switching elements and
the directed arcs in the graph represent communication links
between switching elements.
• Each arc has a weight that represents the cost of sending a
packet between two nodes in a particular direction.
• The objective in short path routing is to find a path between
two nodes that has the smallest total cost, where the total cost
of a path is the sum of the arc costs in that path

Dijkstra s algorithm:
ʼ
1. Source node is initialized and can be indicated as filled circle
2. Initial path cost to neighboring nodes or link cost is computed and these nodes
are relabeled considering source node
3. Examine the all adjacent nodes and finds the smallest label, make it
permanent
4. The smallest label node is now working node ,then step 2,3 are repeated till
the destination node reaches

Bellman-Ford
Bellmon-Ford algorithm is some what similar to Dijkstra’s algorithm but here the shortest
paths from a given source node is computed subject to the constraint that the path contain
at most one link i,e from source node ,at each step least cost path with maximum number
of links are found. Finally the least cost path to each node and the cost of that path is
computed .

3. Distance Vector Routing
• Two dynamic algorithms in particular,
distance
routing and link state routing, are the most popular.
vector
• Historically known as the old ARPANET routing algorithm
(or known as Bellman-Ford algorithm).
• Each router maintains a Distance Vector table containing
the distance between itself and ALL possible destination
nodes. Distances, based on a chosen metric, are computed
using information from the neighbors’ distance vectors.

Distance Vector Algorithm –
1. A router transmits its distance vector to each of its neighbors
in a routing packet.
2. Each router receives and saves the most recently
received
distance vector from each of its neighbors.
3. A router recalculates its distance vector when:
1. It receives a distance vector from a neighbor containing
different information than before.
2. It discovers that a link to a neighbor has gone down.

Example – Consider 3-routers X, Y and Z as shown in
figure. Each router have their routing table. Every routing
table will contain distance to the destination nodes.
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Consider router X , X will share it routing table to
neighbors and neighbors will share it routing table to it to X
and distance from node X to destination will be calculated
using bellmen- ford equation.
Dx(y) = min { C(x,v) + Dv(y)} for each node y ∈ N
As we can see that distance
will be less going from X to
Z when Y is intermediate
node(hop) so it will be
update in routing table X.
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Similarly for Z also
–
Finally the routing table for all is
above–

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Finally the routing table for all –
Note – Distance Vector routing uses UDP(User datagram
protocol) for transportation.

4. Flooding :
• Requires no network information like topology, load
condition
,cost of diff. paths
•Every incoming packet to a node is sent out on every outgoing
like except the one it arrived on.
• For Example in below figure
• A incoming packet to (1) is sent out to (2),(3)
• from (2) is sent to (6),(4) and from (3) it is sent to (4),(5),etc

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Characteristics –
• All possible routes between Source and Destination is tried. A
packet will always get through if path exists
•As all routes are tried, there will be atleast one route which is the
shortest. All nodes directly or indirectly connected are visited
Limitations –
•Flooding generates vast number of duplicate packets, in fact, an
infinite number unless some measures are taken to damp the
process.
•One such measure is to have a hop counter contained in the
header of each packet, which is decremented at each hop, with the
packet being discarded when the counter reaches zero. Ideally,
the hop counter should be initialized to the length of the path
from source to destination.

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• A variation of flooding that is slightly more practical is
selective flooding. In this algorithm the routers do not send
every incoming packet out on every line, only on those lines
that are going approximately in the right direction
• Flooding is not practical in most applications.
Advantages of Flooding :
• Highly Robust, emergency or immediate messages can
(eg military applications)
• Broadcast messages to all the nodes
be sent

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5. Link State Routing
• Distance vector routing algorithm was replaced by an entirely
new algorithm, now called link state routing. Variants of link
state routing are now widely used.
• The idea behind link state routing is simple and can be stated
as five parts. Each router must do the following:
1. Discover its neighbors and learn their network addresses.
2. Measure the delay or cost to each of its neighbors.
3. Construct a packet telling all it has just learned.
4. Send this packet to all other routers.
5. Compute the shortest path to every other router.

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6. Path Vector Routing
• path vector protocol does not rely on the cost of reaching a
given destination to determine whether each path available is
loop free or not. Instead, path vector protocols rely on analysis
of the path to reach the destination to learn if it is loop free or
not.
• A path vector protocol guarantees loop free paths through the
network by recording each hop the routing advertisement
traverses through the network.
• In this case, router A advertises reachability to the
10.1.1.0/24 network to router B. When router B receives this
information, it adds itself to the path, and advertises it to router
C. Router C adds itself to the path, and advertises to router D
that the 10.1.1.0/24 network is reachable in this direction.

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7. Hierarchical Routing:
• As the number of routers becomes large, the overhead
involved in computing, storing, and communicating the
routing table information (e.g., link state updates or least
cost path changes) becomes prohibitive.
• Also an organization should be able to run and administer
its network as it wishes(e.g., to run whatever routing
algorithm it chooses), while still being able to connect its
network to other "outside" networks.
• Clearly, something must be done to reduce the
complexity of route computation in networks as large as
the public Internet.

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• Both of these problems can be solved by aggregating routers
into "regions" or "autonomous systems" (ASs). Routers
within the same AS run the same routing algorithm (e.g., a
LS or DV algorithm) and have full information about each
other.
• The routing algorithm running within an autonomous system
is called an intra-autonomous system routing protocol.
• Routers in an AS that have the responsibility of routing
packets to destinations outside the AS are called gateway
routers.
• The routing algorithm that gateways use to route among the
various ASs is known as an inter-autonomous system
routing protocol.

Fig : Intra-AS and Inter-AS routi34
ng.
• Here, there are three routing ASs, A, B and C. Autonomous system A
has four routers, A.a, A.b, A.c and A.d, which run the intra-AS
routing protocol used within autonomous system A.
• These four routers have complete information about routing paths
within autonomous system A. Similarly, autonomous systems B and
C have three and two routers, respectively.
• Note that the intra-AS routing protocols running in A, B and C
need
not be the same.

The route from A.d to B.b : intra-AS and inter-AS path segments.
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Suppose now that a host h1 attached to router A.d needs to route
a packet to destination h2 in autonomous system B, as shown in
below Figure

Broadcast Routing
• In some applications, hosts need to send messages to many or all
other hosts. Sending a packet to all destinations simultaneously is
called broadcasting.
• One broadcasting method that requires no special features from the
subnet is for the source to simply send a distinct packet to each
destination.
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8. Congestion Control Algorithms
• When too many packets are present in (a part of) the subnet,
performance degrades. This situation is called congestion.
• The network and transport layers share the responsibility
for handling congestion. Since congestion occurs within the
network, it is the network layer that directly experiences it
and must ultimately determine what to do with the excess
packets.
• When the number of packets dumped into the subnet by the
hosts is within its carrying capacity, they are all delivered and
the number delivered is proportional to the number sent.

Algorithms :
•General Principles of Congestion Control
•Congestion Prevention Policies
•Congestion Control in Virtual-Circuit Subnets
•Congestion Control in Datagram Subnets
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General Principles of Congestion Control
• Monitor the system to detect when and
where congestion occurs.
• Pass this information to places where action can
be taken.
• Adjust system operation to correct the problem.

Congestion Prevention Policies
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Congestion Control in Virtual-Circuit Subnets
• In virtual-circuit subnets you can control congestion dynamically.
• One technique that is widely used is admission control.
• The idea is simple: once congestion has been signaled, no
more
virtual circuits are set up until the problem has gone away.
• An alternative approach is to allow new virtual circuits but carefully
route all new virtual circuits around problem areas. For example,
consider the subnet of Fig
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Congestion Control in Datagram Subnets
• Each router can easily monitor the utilization of its output lines
and other resources.
• Whenever u moves above the threshold, the output line enters
a ''warning'' state.
• Each newly-arriving packet is checked to see if its output line
is in warning state. Following are several alternatives for
taking action for warning state.

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These include:
1. Warning bit
2. Choke packets
3. Load shedding
4. Random early discard
5. Traffic shaping
• The first 3 deal with congestion detection and recovery.
The last 2 deal with congestion avoidance

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1. A special bit in the packet header is set by the router to warn
the source when congestion is detected.
2. The bit is copied and piggy-backed on the ACK and sent to
the sender.
3.The sender monitors the number of ACK packets it receives
with the warning bit set and adjusts its transmission rate
accordingly.
Warning Bit

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Choke Packets
1. A choke packet is a control packet generated
at a congested node and transmitted to restrict traffic
flow.
2. The source, on receiving the choke packet must
reduce its transmission rate by a certain percentage.
3. An example of a choke packet is the ICMP Source Quench
Packet.
Hop-by-Hop Choke Packets
4. Over long distances or at high speeds choke packets
are not very effective.
5. A more efficient method is to send to choke packets hop-
by-hop.
6. This requires each hop to reduce its transmission
even before the choke packet arrive at the source

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Load Shedding
1. When buffers become full, routers simply discard packets.
2. Which packet is chosen to be the victim depends on the
application and on the error strategy used in the data link
layer.
3. For a file transfer, for, e.g. cannot discard older packets since
this will cause a gap in the received data.
4. For real-time voice or video it is probably better to throw
away old data and keep new packets.
5. Get the application to mark packets with discard priority.

Random Early Discard (RED)
1. This is a proactive approach in which the router discards one
or more packets before the buffer becomes completely full.
2. Each time a packet arrives, the RED algorithm computes the
average queue length, avg.
3. If avg is lower than some lower threshold, congestion is
assumed to be minimal or non- existent and the packet is
queued.
4. If avg is greater than some upper threshold,
congestion is
assumed to be serious and the packet is discarded.
5. If avg is between the two thresholds, this might indicate the
onset of congestion. The probability of congestion is then
calculated.

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Traffic Shaping
1. Another method of congestion control is to “shape”
the
traffic before it enters the network.
2. Traffic shaping controls the rate at which packets are sent (not
just how many). Used in ATM and Integrated Services
networks.
3. At connection set-up time, the sender and carrier negotiate a
traffic pattern (shape).
Two traffic shaping algorithms are:
4. Leaky Bucket Algorithm
5. Token Bucket Algorithm

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The Leaky Bucket Algorithm used to control rate in a
network. It is implemented as a single- server queue with
constant service time. If the bucket (buffer) overflows then
packets are discarded.
(a) A leaky bucket with water. (b) a leaky bucket with packets.

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1. The leaky bucket enforces a constant output rate
(average rate) regardless of the burstiness of the input.
Does nothing when input is idle.
2. The host injects one packet per clock tick onto the
network. This results in a uniform flow of packets,
smoothing out bursts and reducing congestion.
3. When packets are the same size (as in ATM cells), the
one packet per tick is okay. For variable length packets
though, it is better to allow a fixed number of bytes per
tick.
4. E.g. 1024 bytes per tick will allow one 1024-byte packet
or two 512-byte packets or four 256- byte packets on 1
tick

Token Bucket Algorithm
1. In contrast to the LB, the Token Bucket Algorithm, allows
the output rate to vary, depending on the size of the burst.
2. In the TB algorithm, the bucket holds tokens. To transmit a
packet, the host must capture and destroy one token.
3. Tokens are generated by a clock at the rate of one token
every t sec.
4.Idle hosts can capture and save up tokens (up to the max.
size of the bucket) in order to send larger bursts later.
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Leaky Bucket vs. Token Bucket
1. LB discards packets; TB does not. TB discards tokens.
2. With TB, a packet can only be transmitted if there are
enough tokens to cover its length in bytes.
3. LB sends packets at an average rate. TB allows for
large
bursts to be sent faster by speeding up the output.
4. TB allows saving up tokens (permissions) to send
large
bursts. LB does not allow saving.

UNIT III
NETWORK LAYER – Part 2
IP
addresses,
CIDR,
Su
bnetting,
SuperNetting,
IPv4, Packet
Fragmentation, IPv6
Protocol,
Transition from

• Every device connected to the Internet needs to have an
identifier. Internet Protocol (IP) addresses are the numerical
addresses used to identify a particular piece of hardware
connected to the Internet.
• The two most common versions of IP in use today are Internet
Protocol version 4 (IPv4) and Internet Protocol version
6 (IPv6).
• For IPv4, this pool is 32-bits in size and
contains
4,294,967,296 IPv4 addresses.
• The IPv6 address space is 128-bits(2128) in size, containing
340,282,366,920,938,463,463,374,607,431,768,211,456 IPv6
addresses.

What is an IP address…?
◦ An IP address is a unique global address for a
network interface
- Is a 32 bit long identifier(IPV4)
- Encodes a network number (network prefix)
and a host number
1st Byte
= 128
2nd Byte
= 143
3rd Byte
= 137
4th Byte
= 144
10000000 10001111 10001001 10010000
128.143.137.144.

There are two IP addressing scheme:
◦ 1. Class-full
◦ 2. Classless
In classful addressing the address space is
divided into 5 classes:
A, B, C, D, and E
Prepared By Adugna A.

IPv4 Address
Structure
 Example Class A network address: 114.56.20.33, 255.0.0.0
Network information = 114.
Host information = 56.204.33
 Example Class B network address: 147.12.38.81, 255.255.0.0
Network information = 147.12.
Host information = 38.81
 Example Class C network address: 214.51.42.7, 255.255.255.0
Network information = 214.57.42.
Host information = 7

• Class A addresses are assigned to networks with a very
large number of hosts
• Reserved for governments and large corporations throughout
the world.
• Each class A address supports 16,777,214 hosts.
• The high-order bit(MSB) in a class A address is always set to
zero.
• The next seven bits(completing the first octet) complete the
Network ID
• The remaining 24 bits represent the host ID
Class
A

• Class B addresses are assigned to large- and medium-
sized
companies
• Each Class B address supports 65,534 hosts
•The two high-order bits in a class B address are always
set to binary 1 0.
• The next 14 bits complete the Network ID

• Class C addresses are used for small networks.
–
Addresses
are assigned to groups that meet the
qualifications to obtain Class A and B addresses
– Supports 254 hosts
• The three high-order bits(MSB) in a class C address
are always set to 1 10
• The next 21 bits complete the Network ID

• Class D addresses are reserved for IP multicast addresses. Also
known as multicast addresses.
• Multicasting is the sending of a stream of data (usually audio
and video) to multiple computers simultaneously
 The four high-order bits in a class D address are always set
to binary 1 1 1 0.
 The remaining bits are for the address that interested hosts
recognize.
• Class E addresses are reserved for research, testing.
 The high-order bits in a class E address are set to 1111.
 The Class E range starts where Class D leaves off

Address Class First Network ID Last Network ID
Class A 1.0.0.0 126.0.0.0
Class B 128.0.0.0 191.255.0.0
Class C 192.0.0.0 223.255.255.0
Summary of Usable
Addresses

Classless Inter Domain Routing (CIDR)
• In the Classful addressing the number of Hosts within a
network always remains the same depending upon the
class of the Network.
 Class A network contains 224 Hosts,
 Class B network contains 216 Hosts,
 Class C network contains 28 Hosts
• Now, let’s suppose an Organization requires 214 hosts, then
it must have to purchase a Class B network. In this case,
49152 Hosts will be wasted. This is the major drawback of
Classful Addressing.

• In order to reduce the wastage of IP addresses a new concept
of Classless Inter-Domain Routing is introduced. Now a
days IANA is using this technique to provide the IP addresses.
Whenever any user asks for IP addresses, IANA is going to
assign that many IP addresses to the User.
• Representation: It is as also a 32-bit address, which includes a
special number which represents the number of bits that are
present in the Block Id.
a . b . c . d / n

Rules for forming CIDR Blocks:
1. All IP addresses must be contiguous.
2. Block size must be the power of 2 (2n).
If the size of the block is the power of 2, then it will be
easy to divide the Network. Finding out the Block Id is
very easy if the block size is of the power of 2.
Example:
• If the Block size is 25 then, Host Id will contain 5 bits and
Network will contain 32 – 5 = 27 bits.
1.First IP address of the Block must be evenly divisible by the size
of the block. in simple words, the least significant part should always
start with zeroes in Host Id. Since all the least significant bits
of Host Id is zero, then we can use it as Block Id part.

Example:
Check whether 100.1.2.32 to 100.1.2.47 is a valid IP address block
or not?
1. All the IP addresses are contiguous.
2. Total number of IP addresses in the Block = 16 = 24.
3. 1st IP address: 100.1.2.00100000
Since, Host Id will contains last 4 bits and all the least
significant 4 bits are zero. Hence, first IP address is evenly
divisible by the size of the block.
All the three rules are followed by this Block. Hence, it is
a valid
IP address block.

What is Subnetting?
• Subnetting is a process of dividing a single large network
in multiple smaller networks.
• A single large network is just like a town without any
sector and street address. In such a town, a postman may
take 3 to 4 days in finding a single address. While if town
is divided in sectors and streets, he can easily find any
address in less than one hour.

• Subnetting is used to divide a large IP network in smaller IP
networks known as subnets.
• A default class A, B and C network provides 16777214,
65534, 254 hosts respectively. Having so many hosts in a
single network always creates several issues such as
broadcast, collision, congestion, etc.
• Let’s take a simple example. In a company there are four
development
departments; sales,
management. In
each
production,
and
department there are 50
users.
Company used a private class C IP network. Without any
Subnetting, all computers will work in a single large
network.
Subnetting

company has
departments, it
• Since
four
can divide its
in four
network
subnets.
• Following figure
shows same network
after Subnetting.

Subnetting table
Description Network 1 Network 2 Network 3 Network 4
Network
address
192.168.1.0 192.168.1.64 192.168.1.128 192.168.1.192
valid hosts 192.168.1.1 to
192.168.1.62
192.168.1.65
to
192.168.1.126
192.168.1.129
to
192.168.1.190
192.168.1.193
to
192.168.1.254
Broadcast
address
192.168.1.63 192.168.1.127 192.168.1.191 192.168.1.255

Advantage of Subnetting
•Subnetting reduces network traffic by allowing only
the broadcast traffic which is relevant to the subnet.
• By reducing unnecessary traffic, Subnetting improves overall
performance of the network.
• By blocking a subnet’ traffic in subnet, Subnetting increases
security of the network.
Disadvantage of Subnetting
•Different subnets need an intermediate device known as router
to communicate with each other.
•Subnetting adds complexity in network. An experienced
network administrator is required to manage the subnetted
network.

Supernetting
• Supernetting is the opposite of Subnetting. In subnetting, a
single big network is divided into multiple smaller
subnetworks.
• In Supernetting, multiple networks are combined into a
bigger network termed as a Supernetwork or Supernet.
• Supernetting is mainly used in Route Summarization, where
routes to multiple networks with similar network prefixes are
combined into a single routing entry, with the routing entry
pointing to a Super network, encompassing all the networks.
• This in turn significantly reduces the size of routing tables
and also the size of routing updates exchanged by routing
protocols.

There are some points which should be kept in mind while
supernetting:
1. All the Networks should be contiguous.
2. The block size of every networks should be equal
and
must be in form of 2n.
3. First Network id should be exactly divisible by
whole
size of supernet.
Example – Suppose 4 small networks of class C
200.1.0.0,
200.1.1.0,
200.1.2.0,
200.1.3.0
Build a bigger network which have a single Network Id.

First, lets check whether three condition are satisfied or not:
Contiguous: You can easily see that all network are contiguous
all having size 256 hosts.
Range of first Network from 200.1.0.0 to 200.1.0.255. If you
add 1 in last IP address of first network that is 200.1.0.255 +
0.0.0.1, you will get the next network id that is 200.1.1.0.
Similarly, check that all network are contiguous.
Equal size of all network: As all networks are of class C, so all
of the have a size of 256 which in turn equal to 28.

First IP address exactly divisible by total size:
• When a binary number is divided by 2n then last n bits are the
remainder.
• Hence in order to prove that first IP address is
exactly divisible by while size of Supernet Network.
• In given example first IP is 200.1.0.0 .If last 10 bits of first IP
address are zero then IP will be divisible.
Last 10 bits of first IP address are zero (highlighted by green
color). So 3rd condition is also satisfied.
Therefore, you can join all these 4 networks and can make a
Supernet. New Supernet Id will be 200.1.0.0.

• The network layer protocol in the TCP/IP protocol suite is
currently IPv4 (Internetworking Protocol, version 4).
• IPv4 provides the host-to-host communication
between
systems in the Internet.
• Although IPv4 is well designed, data communication has
evolved since the inception of IPv4 in the 1970s.
• IPv4 has some deficiencies that make it unsuitable for the
fast-growing Internet.
IPv6

Deficiencies:
• Despite all short-term solutions, such as subnetting, classless
addressing, and NAT, address depletion is still a long-term
problem in the Internet.
• The Internet must accommodate real-time audio and video
transmission. This type of transmission requires minimum
delay strategies and reservation of resources not provided in
the IPv4 design.
• The Internet must accommodate encryption and authentication
of data for some applications. No encryption or authentication
is provided by IPv4.
To overcome these deficiencies, IPv6 (Internetworking Protocol,
version 6), also known as IPng (Internetworking Protocol, next
generation), was proposed and is now a standard.

Advantages
The next-generation IP, or IPv6, has some advantages over IPv4
that can be summarized as follows:
Larger address space: An IPv6 address is 128 bits long,
compared with the 32-bit address of IPv4, this is a huge (296)
increase in the address space.
Better header format IPv6 uses a new header format in which
options are separated from the base header and inserted, when
needed, between the base header and the upper-layer data. This
simplifies and speeds up the routing process because most of
the options do not need to be checked by routers.
New options: IPv6 has new options to allow for additional
functionalities.

Advantages
Allowance for extension: IPv6 is designed to allow the
extension of the protocol if required by new technologies or
applications.
Support for resource allocation: In IPv6, the type-of-
service field has been removed, but a mechanism (called
flow label) has been added to enable the source to request
special handling of the packet. This mechanism can be used
to support traffic such as real-time audio and video.
Support for more security: The encryption and
authentication options in IPv6 provide confidentiality and
integrity of the packet.

IPv6 Address
Structure
Feature IPv6
Size of address (bits
or byes per octets)
128 bits, 16 octets
Example address 0000:0000:0000:0000:0000:FFFF:FFFF:0A01:0101
Number of
possible address,
ignoring reserved
values
2128, or roughly 3.4 * 1038

Large address space
New header format
Extensibility
IPV6
Built in Security Better support for QoS
Efficient & hierarchical addressing and
routing infrastructure

IPv6 Packet Format
 Version: 6 for
IPv6
 PayloadLen: the length of
the packet in terms of byte,
excluding the header
 NextHeader: the upper layer
protocol (e.g., TCP or UDP)
or the next extended
header.
 HopLimit: same as
TTL
 SourceAddress
and
DestinationAddres
s
Version TrafficClass Flow Label
PayloadLen NextHeader HopLimit
SourceAddress
DestinationAddress
0 4 12 16
24
31
Next
header/data

TRANSITION FROM IPv4 TO IPv6:
• Because of the huge number of systems on the Internet, the
transition from IPv4 to IPv6 cannot happen suddenly.
• It takes a considerable amount of time before every system
in the Internet can move from IPv4 to IPv6.
• The transition must be smooth to prevent any
problems between IPv4 and IPv6 systems.

Dual Stack
• It is recommended that all hosts, before
migrating
completely to version 6, have a dual stack of protocols.
• In other words, a station must run IPv4 and
IPv6
simultaneously until all the Internet uses IPv6.

Tunneling
• Tunneling is a strategy used when two computers using
IPv6 want to communicate with each other and the packet
must pass through a region that uses IPv4.
• To pass through this region, the packet must have an IPv4
address. So the IPv6 packet is encapsulated in an IPv4
packet when it enters the region, and it leaves its capsule
when it exits the region. It seems as if the IPv6 packet goes
through a tunnel at one end and emerges at the other end. To
make it clear that the IPv4 packet is carrying an IPv6 packet
as data.

Header
Translation
• Header translation is necessary when the majority of the
Internet has moved to IPv6 but some systems still use
IPv4.
• The sender wants to use IPv6, but the receiver does not
understand IPv6. Tunneling does not work in this situation
because the packet must be in the IPv4 format to be
understood by the receiver.
• In this case, the header format must be totally changed
through header translation. The header of the IPv6 packet is
converted to an IPv4 header

•Packet Fragmentation is a process of dividing the datagram into
fragments during its transmission.
•It is done by intermediary devices such as routers at the destination host
at network layer.
•Fragmentation is done by the network layer when the maximum size of
datagram is greater than maximum size of data that can be held a frame i.e.,
its Maximum Transmission Unit (MTU). The network layer divides the
datagram received from transport layer into fragments so that data flow is not
disrupted.
•For example, if a router connects a LAN or WAN, its receives a frame in
the LAN format and sends a frame in the WAN format

MAXIMUM TRANSFER UNIT
 Each data link layer protocol has its own frame format in most
protocol.
When a datagram is encapsulated in a frame, the total size of the
datagram must be less than its maximum size which is defined by the
restriction imposed by the hardware and software used in the network
To make the IPv4 protocol independent of the physical network, the
designers to make the maximum length of the IPv4 datagram equal to
65,535 bytes.

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