Internet Protocol.pdf

Unit-2 Internet Protocol
Prof. D. P. Mishra
Digitally signed by Prof. D. P. Mishra
DN: cn=Prof. D. P. Mishra, o=DURG, ou=BIT, email=dpmishra@bitdurg.ac.in, c=IN
Date: 2021.04.28 11:47:05 +05'30'

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Purpose of IP
• Primary Network communication protocol
• IP relays/transfers network packet called datagrams
• Introduced in 1974 by vint cerf and bob kahn
• IP was datagram service included with TCP for providing
connectionless services
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Primary responsibility ..
• To provide legitimate network address and encapsulation
• Routing packets from one or many IP based networks
• Primary functionality is to provide identification of computer host nd
location service
• IP is main protocol of network layer which is responsible for
exchanging messages/datagrams/packets
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Internet Protocol Version 4
(IPv4)
• Internet Protocol is one of the major protocols in the TCP/IP
protocols suite.
• This protocol works at the network layer of the OSI model and at the
Internet layer of the TCP/IP model.
• Thus this protocol has the responsibility of identifying hosts based
upon their logical addresses and to route data among them
over the underlying network.
• IP provides a mechanism to uniquely identify hosts by an IP
addressing scheme.
• IP uses best effort delivery, i.e. it does not guarantee that packets
would be delivered to the destined host, but it will do its best to
reach the destination.
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IPV4 Header
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Header Details
• VER: Version of the IP protocol (4 bits), which is 4 for IPv4
• HLEN: IP header length (4 bits), which is the number of 32 bit words in the
header. Minimum value for this field is 5 and the maximum is 15
• Type of service: Low Delay, High Throughput, Reliability (8 bits)
• Total Length: Length of header + Data (16 bits), which has a minimum value
20 bytes and maximum is 65,535 bytes
• Identification: Unique Packet Id for identifying the group of fragments of a
single IP datagram (16 bits)
• Flags: 3 flags of 1 bit each : reserved bit (must be zero), do not fragment
flag, more fragments flag (same order)
• Fragment Offset: Specified in terms of number of 8 bytes, which has the
maximum value of 65,528 bytes
• Time to live: Datagram’s lifetime (8 bits), It prevents the datagram to loop in
the network
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Protocol field
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Protocol Hex Value Decimal Value
Reserved 00 0
ICMP 01 1
IGMP 02 2
GGP (Gateway to Gateway) 03 3
IP-in-IP Encapsulation 04 4
TCP 06 6
EGP (Exterior Gateway Protocol) 08 8
UDP 11 17
ESP 32 50
AH 33 51

Header checksum
• Computed over header to provide protection against corruption in
transmission
• Calculated by dividing header bytes in words and then adding them
together
• It only considers header portion not payload
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Other fields
• Source address – Sender address
• Destination address - final destination (receiver)
• Options – Timestamp, record route taken , specify the list of routers
to visit
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ARP , RARP
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The Address Resolution Protocol(ARP) maps a logical address to a physical address.

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RARP

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RARP
• RARP – obsolete Protocols
• BOOTP and others are in use
• RARP allows/supports only IP, No DG & DNS
• BOOTP Supports all

Proxy ARP
• Proxy ARP is a technique by which a proxy server on a given
network answers the Address Resolution Protocol (ARP) queries for
an IP address that is not on that network.
• The proxy is aware of the location of the traffic's destination and
offers its own MAC address as the (ostensibly final) destination.
• Proxy ARP is used between one more networks. In other words, we
can say that Proxy ARP provides data link discovery between
different networks.
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Think about that, PC 1 want to ping PC 4 and it does not have PC 4’s MAC address
in its ARP Cache.
Here, the router has also an ARP Cache. We assume that Router’s ARP Cache has
only its interfaces at the beginning.
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Think about that, PC 1 want to ping PC 4 and it does not have PC 4’s MAC address in its ARP
Cache. Here, the router has also an ARP Cache. We assume that Router’s ARP Cache has
only its interfaces at the beginning.

Firstly PC 1 sends a broadcast ARP Request to learn MAC address
of destination PC 4. With the other PCs in the same network, the first
network side interface of the router will also receive this broadcast.
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Router detects that the destination is not in this network but it knows
the other network. So, router sends an ARP Reply to PC 1 with its
own interface MAC address. This message means that:
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Router checks its ARP Cache and it does not find any
record about PC 4’s IP address and MAC Address. So, it
sends a broadcast ARP Request to the second network.
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PC 4 in the second network, determines that the router that is being looked for is himself. It sends an ARP Reply,
that means :
“This is me!”

BOOTP
• The Bootstrap Protocol (BOOTP) is a computer networking protocol used in Internet Protocol
networks
• BOOTP automatically assign an IP address to network devices from a configuration server.
• The BOOTP was originally defined in RFC 951.
• BOOTP is implemented using the User Datagram Protocol (UDP) for transport protocol,
• BOOTP operates only on IPv4 networks.
• Port number 67 is used by the (DHCP) server for receiving client-requests and port number 68
is used by the client for receiving (DHCP) server responses.
• DHCP is based on BOOTP
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• Port number 67 is used by the server for receiving client-requests and
• Port number 68 is used by the client for receiving (DHCP) server responses.

ICMP
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ICMP
• IP is unreliable protocol.
• Provides connectionless service for delivering datagram.
• IP is not having error correction and reporting mechanism.
• What happens if something goes wrong, what if router discards
packet if it doesn’t find route for the packet.
• IP also lacks in mechanism for lost and management queries.
• ICMP is designed to compensate the above deficiency.
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Position of ICMP in N/W Layer
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• ICMP is network layer protocol
• However its messages are not directly passed to lower layer
• Messages are first encapsulated in IP datagram before going to lower layer.

ICMP Message
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Types of ICMP Messages
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ICMP Error Reporting

ICMP Query Messages
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ICMP Message Format
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• ICMP has 8-byte header and variable size data section
• Although general format of header is different for each message
type but the first four bytes are common to all

Source Quench
• Source Quench is an ICMP based mechanism used by network
devices to inform data sender that the packets can not be forwarded
due to buffers overload.
• When the message is received by a TCP sender, that sender should
decrease its send window to the respective destination in order to
limit outgoing traffic
• Source quench message is request to decrease traffic rate for
messages sending to the host(destination)
• ICMP will take source IP from the discarded packet and informs to
source by sending source quench message
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Source Quenching ..
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• Then source will reduce the speed of transmission so that router will free for congestion.
• When the congestion router is far away from the source the ICMP will send hop by
hop source quench message so that every router will reduce the speed of
transmission.

IGMP
• IP communication involves in two types of communication
• Unicast and multicast
• Unicast is in between sender and receiver one-to-one
• Multicast is one-to-many
• E.g. stock brokers, travel agents and applications like learning and
video on demand
• For Multicasting Class D IP address is used
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Routing Protocol in Computer
Network
• Routing is the process of
selecting a path for traffic in a
network or between or across
multiple networks.
• Broadly, routing is performed in
many types of networks, including
circuit-switched networks, such as
the public switched telephone
network (PSTN), and computer
networks, such as the Internet.
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Delivery
• The network layer examines the handling of packets by the
underlying networks.
• This handling is referred to as delivery of a packet.
• The delivery of packet (source to final destination) can be
achieved by two methods:
1. Direct delivery
2. Indirect Delivery
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Direct delivery
• In this method, the source and destination of the packets are located
on the same network.
• The sender can determine, if the delivery is direct.
• With the help of masking, the sender can extract the network
address of the destination and compares this address with the
addresses of the connected networks.
• If the match is found, then the delivery is direct.
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Indirect Delivery
• In this method, the destination host is not on the same network as
the deliverer. The packet is not delivered directly.
• The packet moves from router to router until it reaches the same
physical network as its final destination.
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Direct vs Indirect
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Administrative Distance
• Administrative Distance (AD) is used to rate the trustworthiness
of routing information received from the neighbor router.
• AD is a numeric value which can range from 0 to 255.
• A smaller Administrative Distance (AD) is more trusted by a
router, therefore the best
• Administrative Distance (AD) being 0 and the worst, 255.
• The route with the least AD will be selected as the best route to
reach the destination remote network and that route will be placed
in the routing table.
• It defines how much reliable a routing protocol is.
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Routing
• To route IP packets, a host or a router has a routing table with entries for each
destination or a combination of destinations.
• A static routing table contains information, which is entered manually.
• The administrator enters the route for each destination into the table.
• Dynamic routing table is updated periodically by using dynamic protocols like
RIP, OSPF or BGP.
• The main function of the network is to route the packets from source to
destination.
• More than one route is possible in every network, however the shortest route
should be selected.
• The shortest route means, a route which passes through the least number of
nodes to reach the destination.
• The routing algorithm is designed to find the shortest root and it is part of a
network software.
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Classification
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Static(non adaptive) Routing
• Routing is done by the Network Administrators manually.
• All the possible paths which are already calculated are loaded into the routing
table.
• This setting will describe the path from a packet to its destination
Pros:
• On the router CPU, there is no processing time (overhead).
• Security guarantees. Suitable for smaller networks
Cons:
• Administrators must be able to understand internetwork on a system and router,
in order to connect and function correctly.
• On large scale computer networks static routing is not suitable for use.
• Inability to respond quickly in case of network failure.
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Dynamic Routing
• The routing process is done by creating an automatic data communication path.
• Dynamic routing can change their routing decision on the basis of some changes
made in the topology.
• Dynamic routing is located at the computer layer network layer in the TCP / IP
Protocol Suites.
Advantage:
• Easier to use than static and default routing.
Cons
• Router workloads become heavy because of updates to the routing table at a
certain time.
• The speed of recognition and completeness of the routing table requires a long
time.
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Default Routing
• The default route establishes a forwarding rule for packets when
no specific address of a next-hop host is available from
the routing table or other routing mechanisms.
• A default route is the route that takes effect when no other route is
available for an IP destination address.
• The default route in IPv4 is designated as 0.0.0.0/0 or simply 0/0
• The default route generally has a next-hop address of another
routing device,
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An autonomous system (AS)
• AS is a network or group of networks
• Under one administrative group or organization
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Intradomain vs Interdomain
• Routing inside an autonomous system is referred to as intra-
domain routing, e.g. Distance vector
• Routing between two or more autonomous systems can be referred to
as inter-domain routing, e.g. Path Vector
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Intra-domain Routing Inter-domain Routing
Routing takes place within an
autonomous network.
Routing takes place between the
two autonomous networks.
This protocol ignores the internet outside
the autonomous system.
This protocol assumes that internet consists of
a collection of interconnected autonomous
systems.
Protocols for Intra-domain routing are
called as interior gateway protocols.
Protocol for Inter-domain routing are also
called as exterior gateway protocols.
Examples: RIP and OSPF etc. Example: BGP

Distance Vector Routing
• Distance vector routing is the dynamic routing algorithm and also
known as Bellman-Ford routing algorithm and Ford-
Fulkerson algorithm.
• It was designed for small network topologies.
• In this algorithm, node router constructs a table containing the
distance (total cost of path) to all other nodes and distributes that
vector to its immediate neighbors.
• For distance vector routing, it is assumed that each node knows the
cost of the link to each of its directly connected neighbors.
• A link, which is 'down' (which is not working) is assigned as an
infinite cost.
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Distance Vector Routing ..
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 Every node sends a message to its directly connected neighbors For example: A sends its information
to B and F.
 After communicating to each directly connected node, the shortest path can be easy to compute (as
shown in above table).

Advantages of distance Vector
• Distance vector routing protocol is easy to implement in small
networks.
• Debugging is very easy in the distance vector routing protocol.
• This protocol has a very limited redundancy in a small network.
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Issues with the Distance Vector
Routing are:
• It takes long time for convergence due to growth in the
network (slower to converge than link state)
• It is at risk from the count-to-infinity problem.
• Vulnerability to the 'Count-to-Infinity' problem is a serious issue
with the distance vector.
• It creates more traffic than link state since a hop count change
must be propagated to all routers and processed on each router.
•
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Link state routing
• It is a dynamic type routing algorithm.
• In this method, one or more routers can be connected by using LAN.
• When a router is booted, it sends a special request (HELLO packet) message on
each point-to-point line.
• Then second router sends back a reply and asks who is it and the communication
starts.
• To determine the cost of line or path, the router sends an ECHO packet over the
line which the other router is required to send back immediately.
• By measuring the round-trip time and dividing it by two, the router (sender) can
get a reasonable estimate of the delay.
• Link state packet can be constructed periodically or after the occurrence of some
significant event. For example: if a line or neighbor is down or it may be coming
back.
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Example.
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Basic algorithm to distribute the
link state packets:
• Each state packet has a sequence number and it is incremented
for each sent packet.
• Routers can track all the source routers and sequence.
• When a new link state packet arrives, it is checked against the
list of packets already entered.
• If the packet is new, it is forwarded on all lines (except on
which it is arrived ie flooding) and discarded, if the packet is
duplicate.
• If the sequence number is lower (than the highest one), it is
rejected.
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Changes to improve basic algo
• Once the router accumulates full set of link state packets, it can
construct the entire subnet graph and
• Dijkshtra's algorithm can be used to construct the shortest path to
all possible destination.
• Link state routing protocol uses event driven updates rather than
periodic updates.
• Link state routing protocol is widely used in actual networking
system.
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Routing Information Protocol
(RIP).
• The RIP is an intra-domain routing protocol.
• It is based on distance vector routing.
• In Implementation of RIP, the following steps are taken into
consideration:
1. The routers have routing tables, but network does not have routing table.
2. The destination in routing table is a network, this states that the first
column defines a network address.
3. The metric in RIP is called a hop count.
4. Infinity is defined as 16, which means that any route in an
autonomous system using RIP cannot have more than 15 hops.
5. The next-node column defines the address of the router to which the
packet is to be sent to reach its destination.
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RIP ..
• Dynamic Routing Protocol
• It is a distance vector routing protocol
• It has AD value 120 and works on the application layer of OSI
model.
• RIP uses port number 520
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Working of RIP
• If there are 8 routers in a network
where
• Router 1 wants to send the data to
Router 3.
• If the network is configured with RIP, it
will choose the route which has the least
number of hops.
• There are three routes in the above
network, i.e., Route 1, Route 2, and
Route 3.
• The Route 2 contains the least number
of hops, i.e., 2 where Route 1 contains 3
hops, and Route 3 contains 4 hops,
• So RIP will choose Route 2.
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Let's look at another example
• Suppose R1 wants to send the
data to R4.
• There are two possible routes to
send data from r1 to r2.
• As both the routes contain the
same number of hops, i.e., 3, so
• RIP will send the data to both the
routes simultaneously.
• This way, it manages the load
balancing, and data reach the
destination a bit faster.
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How RIP updates its Routing
table
The following timers are used to update the routing table:
RIP update timer : 30 sec
• The routers configured with RIP send their updates to all the neighboring routers every 30
seconds.
RIP Invalid timer : 180 sec
• The RIP invalid timer is 180 seconds, which means that if the router is disconnected from the
network or some link goes down, then the neighbor router will wait for 180 seconds to take the
update.
• If it does not receive the update within 180 seconds, then it will mark the particular route as not
reachable.
IP Flush timer : 240 sec
• The RIP flush timer is 240 second which is almost equal to 4 min means that
• If the router does not receive the update within 240 seconds then the neighbor route will remove
that particular route from the routing table which is a very slow process as 4 minutes is a long
time to wait.
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Advantages of RIP
• It is easy to configure
• It has less complexity
• The CPU utilization is less.
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Disadvantages of RIP
• In RIP, the route is chosen based on the
hop count metric.
• If another route of better bandwidth is
available, then that route would not be
chosen.
• Let's understand this scenario through an
example.
• We can observe that Route 2 is chosen in
the figure as it has the least hop count.
• The Route 1 is free and data can be
reached more faster; instead of this, data
is sent to the Route 2 that makes the
Route 2 slower due to the heavy traffic.
• This is one of the biggest disadvantages of
RIP.
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Disadvantages of RIP..
• The RIP is a classful routing protocol, so it does not support the VLSM (Variable
Length Subnet Mask).
• It broadcasts the routing updates to the entire network that creates a lot of traffic.
• In RIP, the routing table updates every 30 seconds. Whenever the updates occur, it
sends the copy of the update to all the neighbors except the one that has caused the
update.
• It faces a problem of Slow convergence. Whenever the router or link fails, then it often
takes minutes to stabilize or take an alternative route; This problem is known as Slow
convergence.
• RIP supports maximum 15 hops which means that the maximum 16 hops can be
configured in a RIP
• The Administrative distance value is 120 (Ad value). If the Ad value is less, then the
protocol is more reliable than the protocol with more Ad value.
• The RIP protocol has the highest Ad value, so it is not as reliable as the other routing
protocols.
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Source - cisco

D. V . Summary ..
• Assume:
 Each router knows only address/cost of neighbors
• Goal:
 Calculate routing table of next hop information for each destination
at each router
• Idea:
 Tell neighbors about learned distances to all destinations
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DV Algorithm
• Each router maintains a vector of costs to all destinations
• Initialize neighbors with known cost, others with infinity
• Periodically send copy of distance vector to neighbors
• On reception of a vector, if neighbors path to a
destination plus neighbor cost is better, then switch to
better path
• Update cost in vector and next hop in routing table
• Assuming no changes, will converge to shortest paths
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DV Example – Initial Table at A
D
G
A
F
E
B
C
Dest Cost Next
B 1 B
C 1 C
D  -
E 1 E
F 1 F
G  -
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DV Example – Final Table at A
• Reached in a single iteration … simple example
D
G
A
F
E
B
C
Dest Cost Next
B 1 B
C 1 C
D 2 C
E 1 E
F 1 F
G 2 F
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What if there are changes?
• One scenario: Suppose link between F and G fails
1. F notices failure, sets its cost to G to infinity and tells A
2. A sets its cost to G to infinity too, since it learned it from F
3. A learns route from C with cost 2 and adopts it
D
G
A
F
E
B
C
XXXXX
Dest Cost Next
B 1 B
C 1 C
D 2 C
E 1 E
F 1 F
G 3 C
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• Simple example
 Costs in nodes are to reach Internet
• Now link between B and Internet fails …
Count To Infinity Problem
Internet
A/2 B/1
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• B hears of a route to the Internet via A with cost 2
• So B switches to the “better” (but wrong!) route
update
Internet
A/2 B/3
XXX
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• A hears from B and increases its cost
update
Internet
A/4 B/3
XXX
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• B hears from A and (surprise) increases its cost
• Cycle continues and we “count to infinity”
• Packets caught in the crossfire loop between A and B
update
Internet
A/4 B/5
XXX
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Split Horizon
• Solves trivial count-to-infinity problem
• Split horizon is a method of preventing a routing loop in a network.
• The basic principle is simple: Information about the routing for a
particular packet is never sent back in the direction from which
it was received.
• Split horizon can be achieved by means of a technique called poison
reverse
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Poison reverse
• A poison reverse is a way in which a gateway node tells its
neighbor gateways that one of the gateways is no longer
connected.
• To do this, the notifying gateway sets the number of hops to the
unconnected gateway to a number that indicates "infinite"
(meaning "You can't get there").
• Since RIP allows up to 15 hops to another gateway, setting the
hop count to 16 would mean "infinite.“
• This is the equivalent of route poisoning all possible reverse
paths
• Split horizon with poison reverse is more effective than simple
split horizon in networks with multiple routing paths
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RIP – More Details
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RIP - Routing Information
Protocol
• RIP supports dynamic routing
• Based on Distance vector uses hop count as metric
• A simple intradomain/IGP(Interior gateway Protocol)
• Open Standard , based on distance vector
• Classful routing protocol (Doesn’t support subnetting)
• Each router advertises its distance vector every 30 seconds (or
whenever its routing table changes) to all of its neighbors
• Maximum hop count is 15, with “16” equal to “”
• Administrative distance (AD Value) is 120
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RIPv1
RIP Characteristics
 A Classful, Distance Vector (DV) routing protocol
 Metric = hop count
 Routes with a hop count > 15 are unreachable
 Updates are broadcast every 30 seconds
 Used for smaller network
 Router rip command is used for configuring router
6th
Sem
CSE
-
Internetworking
With
TCP/IP

RIPv1 Packet Format
IP header UDP header RIP Message
Command Version Set to 00...0
32-bit address
Unused (Set to 00...0)
address family Set to 00.00
metric (1-16)
one
route
entry
(20
bytes)
Up to 24 more routes (each 20 bytes)
32 bits
One RIP message can
have up to 25 route entries
1: request
2: response
2: for IP
0…0: request full rou-
ting table
Address of destination
Cost (measured in hops)
1: RIPv1
6th
Sem
CSE
-
Internetworking
With
TCP/IP

RIPv2
• RIPv2 is an extends RIPv1:
 Subnet masks are carried in the route information
 Authentication of routing messages
 Route information carries next-hop address
 Exploites IP multicasting
• Extensions of RIPv2 are carried in unused fields of RIPv1 messages
6th
Sem
CSE
-
Internetworking
With
TCP/IP

RIPv2 Packet Format
IP header UDP header RIP Message
Command Version Set to 00...0
32-bit address
address family Set to 00.00
metric (1-16)
one
route
entry
(20
bytes)
32 bits
One RIP message can
have up to 25 route entries
1: request
2: response
2: for IP
0…0: request full rou-
ting table
Address of destination
Cost (measured in hops)
2: RIP v
6th
Sem
CSE
-
Internetworking
With
TCP/IP

RIPv2 Packet Format
IP header UDP header RIPv2 Message
Command Version Set to 00.00
IP address
Subnet Mask
address family route tag
Next-Hop IP address
metric (1-16)
one
route
entry
(20
bytes)
32 bits
Used to carry information
from other routing
protocols (e.g.,
autonomous system
number)
Identifies a better next-hop
address on the same
subnet than the advertising
router, if one exists
(otherwise 0….0)
2: RIPv2
Subnet mask for IP
address
6th
Sem
CSE
-
Internetworking
With
TCP/IP

RIP Timers
6th
Sem
CSE
-
Internetworking
With
TCP/IP
Update Timer 30 Sec
Hold on timer 180 Sec
Invalid Timer (30 +
150=180 Sec)
Flush Timer(180
+60=240 Sec) - Route is
purged after 4 min
• Invalid Timer : specifies how long a routing entry can be in the routing table without being updated. This is also called
as expiration
• Flush timer : controls the time between the route is invalidated or marked as unreachable and removal of entry from
the routing table
• hold-on timer: is started per route entry, when the hop count is changing from lower value to higher value. This allows
the route to get stabilized.

RIP Messages
• This is the operation of RIP in routed.
• Dedicated port for RIP is UDP port 520.
• Two types of messages:
 Request messages
 used to ask neighboring nodes for an update
 Response messages
 contains an update
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Routing with RIP
• Initialization: Send a request packet (command = 1, address
family=0..0) on all interfaces:
 RIPv1 uses broadcast if possible, 255.255.255.255
 RIPv2 uses multicast address 224.0.0.9, if possible
• Requesting routing tables from neighboring routers
• Request received: Routers that receive above request send their
entire routing table
• Response received: Update the routing table
• Typically, there is a routing daemon (routed) that is an application
layer process that provides access to routing tables.
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Routing with Rip Cont.
• Regular routing updates: Every 30 seconds, send all or part of
the routing tables to every neighbor in an response message
• Triggered Updates: Whenever the metric for a route change, send
entire routing table.
• If a router does not hear from its neighbor once every 180 seconds,
the neighbor is deemed unreachable.
6th
Sem
CSE
-
Internetworking
With
TCP/IP

RIP Convergence
• Takes more time to converge
• RIP requires less CPU power and RAM than other routing protocols
• Router advertises details to its neighbors
• Routing by rumors, similar to rumor spread by peoples living in
locality/neighbors
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Security
• Issue: Sending bogus routing updates to a router
• RIPv1: No protection
• RIPv2: Simple authentication scheme
6th
Sem
CSE
-
Internetworking
With
TCP/IP

RIP Security
IP header UDP header RIPv2 Message
Command Version Set to 00.00
Password (Bytes 0 - 3)
0xffff Authentication Type
Password (Bytes 8- 11)
Authetication
32 bits
2: plaintext
password
6th
Sem
CSE
-
Internetworking
With
TCP/IP

RIPV1 vs RIPV2
RIP V1
• Classful i.e. VLSM not supported
• No authentication
• Uses broadcast address as
255.255.255.255
• Max hopcount is 15
• Periodic update is of 15
RIP V2
• Classless (CIDR/VLSM) Support
• Authentication is supported
• Uses multicast address 224.0.0.9
• In todays scenario only RIPV2 is used
even
• RIPV1 is removed from CISCO
Certification
6th
Sem
CSE
-
Internetworking
With
TCP/IP

RIP Advantages
• Easy to configure
• No Design constraint
• No Complexity
• Less overhead
6th
Sem
CSE
-
Internetworking
With
TCP/IP

RIP Disadvantages
• RIP takes a long time to stabilize / slow convergence
• Work only on hop count
• Bandwidth utilization is high as routing table entry is heared after
every 30 Sec
• RIP has all the problems of distance vector algorithms, e.g., count-to-
Infinity
 RIP uses split horizon to avoid count-to-infinity
• Not scalable as - The maximum path in RIP is 15 hops
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Areas in AS(Autonomous System)
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Links specific to OSPF
• In OSPF connection is called as link
• There are four types of links
 Point-to-Point link
 Transient link
 Stub link
 Virtual link
6th
Sem
CSE
-
Internetworking
With
TCP/IP

1. Point-to-Point Link
• It connects with the help of two routers without any host or router as
a mediator.
• In this type of link, there is no need to assign a network address.
• Graphically, the nodes are represented as nodes and the link is
represented by bidirectional edge connecting the nodes.
6th
Sem
CSE
-
Internetworking
With
TCP/IP

2. Transient link
• It is a network with several
routers attached to it.
• The data can enter through any
one of the routers and pass
through any router.
• The LAN or WAN with two or
more routers are the examples of
the transient link.
6th
Sem
CSE
-
Internetworking
With
TCP/IP

3. Stub link
• It is a network connected with
only one router.
• The data packets enter the
network through this single router
and leave the network through
this same router.
6th
Sem
CSE
-
Internetworking
With
TCP/IP

4. Virtual link
• Virtual link is created by the administrator, when the link between
two routers is disconnected.
6th
Sem
CSE
-
Internetworking
With
TCP/IP

OSPF(Open Shortest Path First)
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Open Shortest Path First (OSPF)
• It is an intra-domain routing protocol based on link state routing.
• To handle routing efficiently, OSPF divides autonomous systems into different areas.
• Areas are the collection of networks, hosts and routers all contained within an
autonomous system.
• An autonomous system can be divided into many different areas.
• All networks inside an area must be connected.
• Routers inside an area flood is considered as the area with routing information.
• At the border of an area, special routers called as area border routers summarize the
information about the area and send it to other areas.
• There is a special area, which is called as backbone and
• All the areas inside an autonomous system must be connected with backbone.
• Backbone serves as primary area and the other areas are served as secondary areas
6th
Sem
CSE
-
Internetworking
With
TCP/IP

OSPF ..
• The routers inside the backbone are called as backbone routers.
• If the connectivity between the backbone and an area is broken, it is
necessary to create a virtual link between routers. The administrator
creates it.
• The OSPF protocol allows the administrator to assign a cost,
called as the metric to each route.
• The metric can be assigned on the type of services like minimum
delay, maximum throughput, etc.
• The router can have multiple routing tables based on different
services.
• In OSPF, a connection is called as link.
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Open Shortest Path First (RFC 1247)
• Uses IP, has a value in the IP Header (8 bit protocol field)
• Interior routing protocol, its domain is also an autonomous system
• Divides an AS into areas
• Metric based on type of service
 Minimum delay (rtt), maximum throughput, reliability, etc..
Unit-3
Comp
Network
by
:
Prof.
D.
P.
Mishra
BITD

OSPF
• IRP/IGP
• Divides AS in different Areas
• Router inside area floods area with routing info
• ABR summarizes the routing info of concern area
• All the areas in AS are connected to backbone area in AS
Unit-3
Comp
Network
by
:
Prof.
D.
P.
Mishra
BITD

OSPF (type of links)
Unit-3
Comp
Network
by
:
Prof.
D.
P.
Mishra
BITD

Point-to-point Link
Unit-3
Comp
Network
by
:
Prof.
D.
P.
Mishra
BITD
Point –to – point link defines direct connection
between routers and it can be represented as
graph with link having bidirectional arrow

Transient Link
Unit-3
Comp
Network
by
:
Prof.
D.
P.
Mishra
BITD
This link defines network to which multiple routers are attached, in
this type of network multiple routers are connected to common
network and they have many neighbors

Stub Links
Unit-3
Comp
Network
by
:
Prof.
D.
P.
Mishra
BITD
This link is special case of transient link, which defines a
network with only one router connected to it, packet
enters and leave the network using single link

Virtual Links
Unit-3
Comp
Network
by
:
Prof.
D.
P.
Mishra
BITD
When the link between two routers is broken, a new link
has to be established by the administrator, which is known
as virtual link

OSPF Background ..
• Link state/Shortest Path First Technology
• Dynamic Routing
• Fast Convergence
• Route authentication

OSPF (link state advertisement)
Router Link
Network Link
Unit-3
Comp
Network
by
:
Prof.
D.
P.
Mishra
BITD

OSPF (LSA cont.)
Summary link to Network
Summary link to AS boundary router
External Link
Unit-3
Comp
Network
by
:
Prof.
D.
P.
Mishra
BITD

DR & BDR
• OSPF uses
a DR (Designated
Router)
and BDR (Backup
Designated Router) on
each multi-access
network. ...
• DR and BDR act as a
central point for
exchanging
of OSPF information
between multiple
routers on the same,
multi-access broadcast
network segment.
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Shortest Path Calculation
Unit-3
Comp
Network
by
:
Prof.
D.
P.
Mishra
BITD

Shortest Path Calculations ..
Unit-3
Comp
Network
by
:
Prof.
D.
P.
Mishra
BITD
3
2
1
4 5
4
4
8
7
3
Visited 1 2 3 4 5
∞ ∞ ∞ ∞ ∞
{1} 0 4 ∞ 8 ∞
{1,2} 0 4 7 8 ∞
{1,2,3} 0 4 7 8 ∞
{1,2,3,4} 0 4 7 8 15

Link State Algorithm
• Each router contains a database containing a
map of the whole topology
 Links
 Their state (including cost)
• All routers have the same information
• All routers calculate the best path to every
destination
• Any link state changes are flooded across the
network
 “Global spread of local knowledge”

Link State Routing
• Automatic neighbour discovery
 Neighbours are physically connected routers
• Each router constructs a Link State Packet (LSP)
 Distributes the LSP to neighbours…
 …using an LSA (Link State Announcement)
• Each router computes its best path to every
destination
• On network failure
 New LSPs are flooded
 All routers recompute routing table

Low Bandwidth Requirements
• Only changes are propagated
• Multicast used on multi-access broadcast
networks
 224.0.0.5 used for all OSPF speakers
 224.0.0.6 used for DR and BDR routers
FDDI
Dual Ring
R1
LSA
X
LSA

“Shortest Path First”
• The optimal path is determined by the sum of
the interface costs
FDDI
Dual Ring
FDDI
Dual Ring
N1
N2 N3
N4
N5
R1
R2
R3
R4
Cost = 1 Cost = 1
Cost = 10
Cost = 10
Cost = 10

OSPF: How it works
• Hello Protocol
 Responsible for establishing and maintaining
neighbour relationships
 Elects Designated Router on broadcast networks
FDDI
Dual Ring
Hello
Hello
Hello

OSPF: How it works
• Hello Protocol
 Hello Packets sent periodically on all OSPF enabled
interfaces
 Adjacencies formed between some neighbours
• Hello Packet
 Contains information like Router Priority, Hello
Interval, a list of known neighbours, Router Dead
Interval, and the network mask

OSPF: How it works
• Trade Information using LSAs
 LSAs are added to the OSPF database
 LSAs are passed on to OSPF neighbours
• Each router builds an identical link state database
• SPF algorithm run on the database
• Forwarding table built from the SPF tree

OSPF: How it works
• When change occurs:
 Announce the change to all OSPF neighbours
 All routers run the SPF algorithm on the revised database
 Install any change in the forwarding table

Types of OSPF packets and header format
Unit-3
Comp
Network
by
:
Prof.
D.
P.
Mishra
BITD

6th
Sem
CSE
-
Internetworking
With
TCP/IP
• Link State Update packets are OSPF packet type 4.
• These packets implement the flooding of link state advertisements.
• Each Link State Update packet carries a collection of link state advertisements one hop further
from its origin.
• Several link-state advertisement may be included in a single packet.

Advantages of OSPF:
• Biggest advantage of OSPF over EIGRP is that it will run on any
device as its based on open standard
• OSPF is an open standard, not related to any particular vendor.
• It uses the SPF algorithm, developed by Dijkstra
• OSPF provide a loop-free topology.
• It provides fast convergence with triggered updates
• It supports classless / VLSM.
• Supports authentication
Unit-3
Comp
Network
by
:
Prof.
D.
P.
Mishra
BITD
Enhanced Interior Gateway Routing Protocol (EIGRP) is an advanced distance-vector
routing protocol that is used in computer network for automating routing decisions and
configuration. (Developed by CISCO)

Disadvantages of OSPF
• It requires extra CPU processing to run the SPF algorithm
• It is bit complex to configure and more difficult to troubleshoot.
• OSPF maintains multiple copies of routing information, increasing
the amount of memory needed.
• OSPF routers check the status of other routers on the network by
sending a small hello packet at regular intervals.
• If a router does not respond to the hello packet, it is assumed dead,
and routing updates are sent to every other router by using a
multicast address.
Unit-3
Comp
Network
by
:
Prof.
D.
P.
Mishra
BITD

What Is a Router Module? .
• A router is a small device that brings together numerous networks.
• In terms of the seven layer OSI model of computer networking, a router is
considered a "Layer 3" gateway device; this means that it can move data from its
origin to its destination using one or more networks.
• In enterprise situations, a modular device has expansion slots that allow the
user the ability to add new modules as needed.
• The majority of modular devices come with a set number of fixed ports along
with the expansion slots.
• When choosing a router, selecting the type and number of ports is a major
decision. A user must ask themselves if they would purchase a router with:
• Just enough ports for today's needs?
• Both UTP and fiber ports?
• A mixture of UTP speeds.
6th
Sem
CSE
-
Internetworking
With
TCP/IP

What Is a Router Module?..
• The user must consider carefully how many fiber ports and UTP ports are needed. At
the same time, they must also consider how many Gbps are needed as well as
bandwidth requirements.
• The modular devices come with expansion slots that give the user the flexibility to
add more modules as requirements change.
• Eg
• Ethernet port modules
• Broadband Modules
• Serial WAN Interface Module
• ISDN(BRI) Module
• Voice Modules
• SIP Proxy Module
• Analog and Digital Voice / Fax Module
6th
Sem
CSE
-
Internetworking
With
TCP/IP

IP Addressing
6th
Sem
CSE
-
Internetworking
With
TCP/IP

IPv4 supports 3-types of addressing
modes.
• Unicast Addressing Mode:
• Broadcast Addressing Mode:
• Multicast Addressing Mode:
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Unicast Addressing Mode:
• In this mode, data
is sent only to one
destined host.
• The Destination
Address field
contains 32- bit IP
address of the
destination host.
• Here the client
sends data to the
targeted server:
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Broadcast Addressing Mode:
• In this mode, the packet is
addressed to all the hosts in
a network segment.
• The Destination Address
field contains a special
broadcast address,
i.e. 255.255.255.255.
• When a host sees this
packet on the network, it is
bound to process it.
• Here the client sends a
packet, which is
entertained by all the
Servers:
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Multicast Addressing Mode:
• This mode is a mix of the
previous two modes, i.e.
the packet sent is
destined neither to a
single host nor all the
hosts on the segment.
• In this packet, the
Destination Address
contains a special
address which starts
with 224.x.x.x and can
be entertained by more
than one host.
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Hierarchical Addressing Scheme
• IPv4 uses hierarchical addressing scheme. An IP address, which is
32-bits in length, is divided into two or three parts as depicted:
• A single IP address can contain information about the network and
its sub-network and ultimately the host.
• This scheme enables the IP Address to be hierarchical where a
network can have many sub-networks which in turn can have many
hosts.
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Subnet Mask
• It is very necessary to distinguish both.
• For this, routers use Subnet Mask, which is as long as the size of the
network address in the IP address.
• Subnet Mask is also 32 bits long. If the IP address in binary is ANDed
with its Subnet Mask, the result yields the Network address.
• For example, say the IP Address is 192.168.1.152 and the Subnet Mask
is 255.255.255.0 then:
• It can be identified now that 192.168.1.0 is the Network number and
192.168.1.152 is the host on that network.
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Binary Representation
• The positional value method is the simplest form of converting
binary from decimal value.
• IP address is 32 bit value which is divided into 4 octets.
• A binary octet contains 8 bits and the value of each bit can be
determined by the position of bit value '1' in the octet.
6th
Sem
CSE
-
Internetworking
With
TCP/IP
• Positional value of bits is determined by 2 raised to power (position – 1), that is the value of a bit
1 at position 6 is 2^(6-1) that is 2^5 that is 32.
• The total value of the octet is determined by adding up the positional value of bits. The value of
11000000 is 128+64 = 192.

6th
Sem
CSE
-
Internetworking
With
TCP/IP
Some examples
are
shown in the table

IPv4 Addressing system is
divided into five classes of IP
• All the five classes are identified by the first octet of IP Address.
• Internet Corporation for Assigned Names and Numbers is
responsible for assigning IP addresses.
• The first octet referred here is the left most of all.
• The octets numbered as follows depicting dotted decimal notation of
IP Address:
6th
Sem
CSE
-
Internetworking
With
TCP/IP
The number of networks and the number
of hosts per class can be derived by this
formula:

Class A Address
• The first bit of the first octet is always set to 0 (zero).
• Thus the first octet ranges from 1 – 127, i.e.
6th
Sem
CSE
-
Internetworking
With
TCP/IP
• Class A addresses only include IP starting from 1.x.x.x to 126.x.x.x only. The IP range 127.x.x.x is
reserved for loopback IP addresses.
• The default subnet mask for Class A IP address is 255.0.0.0 which implies that Class A
addressing can have 126 networks (27-2) and 16777214 hosts (224-2).
• Class A IP address format is thus: 0NNNNNNN.HHHHHHHH.HHHHHHHH.HHHHHHHH

Class B Address
• An IP address which belongs to class B has the first two bits in the first
octet set to 10, i.e
• Class B IP Addresses range from 128.0.x.x to 191.255.x.x.
• The default subnet mask for Class B is 255.255.x.x.
• Class B has 16384 (214) Network addresses and 65534 (216-2) Host
addresses.
• Class B IP address format is:
10NNNNNN.NNNNNNNN.HHHHHHHH.HHHHHHHH
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Class C Address
• The first octet of Class C IP address has its first 3 bits set to 110,
that is:
• Class C IP addresses range from 192.0.0.x to 223.255.255.x.
• The default subnet mask for Class C is 255.255.255.x.
• Class C gives 2097152 (221) Network addresses and 254 (28-2) Host
addresses.
• Class C IP address format
is: 110NNNNN.NNNNNNNN.NNNNNNNN.HHHHHHHH
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Class D Address
• Very first four bits of the first octet in Class D IP addresses are set
to 1110, giving a range of:
• Class D has IP address rage from 224.0.0.0 to 239.255.255.255.
• Class D is reserved for Multicasting. In multicasting data is not
destined for a particular host, that is why there is no need to extract
host address from the IP address, and Class D does not have any
subnet mask.
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Class E Address
• This IP Class is reserved for experimental purposes only for R&D or
Study.
• IP addresses in this class ranges from 240.0.0.0 to 255.255.255.254.
• Like Class D, this class too is not equipped with any subnet mask.
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Summary
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Problems with Classful Addressing:
• The problem with this classful addressing method is that
millions of class A address are wasted,
many of the class B address are wasted,
whereas, number of addresses available in class C is so small that it
cannot cater the needs of organizations.
Class D addresses are used for multicast routing, and are therefore
available as a single block only.
Class E addresses are reserved.
• Since there are these problems,
• Classful networking/addressing was replaced by Classless
Inter-Domain Routing (CIDR) in 1993.
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Subnetting
156
IP
Subnetting
&
Supernetting
-
Prof.
D.
P.
Mishra

Subnetting
 Creates multiple logical networks that exist within a single Class
A, B, or C network.
 If you do not subnet, you will only be able to use one network from
your Class A, B, or C network, which is unrealistic
 Each data link on a network must have a unique network ID, with
every node on that link being a member of the same network
157
IP
Subnetting
&
Supernetting
-
Prof.
D.
P.
Mishra

IPv4 - Subnetting
• Each IP class is equipped with its own default subnet mask which
bounds that IP class to have prefixed number of Networks and
prefixed number of Hosts per network.
• Classful IP addressing does not provide any flexibility of
having less number of Hosts per Network or more Networks per IP
Class.
• CIDR or Classless Inter Domain Routing provides the flexibility
of borrowing bits of Host part of the IP address and using them as
Network in Network, called Subnet.
• By using Subnetting, one single Class A IP address can be used
to have smaller sub-networks which provides better network
management capabilities.
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Subnetting.
• The process of dividing a single network into multiple sub networks
is called as Subnetting.
• The sub networks so created are called as subnets.
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Advantages of subnetting
The main advantages of Subnetting a network are-
 It improves the security.
 The maintenance and administration of subnets is easy.
 Reduced network traffic
 Optimized network performance
Subnet ID-
 Each subnet has its unique network address known as its Subnet ID.
 The subnet ID is created by borrowing some bits from the Host ID part of the IP Address.
 The number of bits borrowed depends on the number of subnets created.
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Types of Subnetting
6th
Sem
CSE
-
Internetworking
With
TCP/IP

1. Fixed Length Subnetting
• Fixed length Subnetting also called as classful
Subnetting divides the network into subnets where-
 All the subnets are of same size.
 All the subnets have equal number of hosts.
 All the subnets have same subnet mask.
6th
Sem
CSE
-
Internetworking
With
TCP/IP

2. Variable Length Subnetting-
• Variable length Subnetting also called as classless
Subnetting divides the network into subnets where-
• All the subnets are not of same size.
• All the subnets do not have equal number of hosts.
• All the subnets do not have same subnet mask.
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Example-01
Consider-
• We have a big single network having IP Address
200.1.2.0.
• We want to do Subnetting and divide this
network into 2 subnets.
• Clearly, the given network belongs to class C.
• For creating two subnets and to represent their
subnet IDs, we require 1 bit.
• So, We borrow one bit from the Host ID part.
• After borrowing one bit, Host ID part remains
with only 7 bits.
6th
Sem
CSE
-
Internetworking
With
TCP/IP

How to create subnets
 Determine the number of required network IDs:
 One for each subnet
 One for each wide area network connection
 Determine the number of required host IDs per subnet:
 One for each TCP/IP host
 One for each router interface
 Based on the above requirements, create the following:
 One subnet mask for your entire network
 A unique subnet ID for each physical segment
 A range of host IDs for each subnet
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Subnetting
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Supernetting
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Prof.
D.
P.
Mishra

Subnetting a Class A/B/C Address
• How many subnets does the chosen subnet mask produce?
• How many valid hosts per subnet are available?
• What are the valid subnets?
• What’s the broadcast address of each subnet?
• What are the valid hosts in each subnet?
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Subnetting
&
Supernetting
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D.
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Mishra

Formula
1. No of subnets = 2x
- Where x is no of bits borrowed
2. No. of host = 2y – 2
- Where Y is no of o’s
3. Magic no or blocksize = Total no of addresses
Magic no/Block Size = 256 – Mask
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Subnetting
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Supernetting
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D.
P.
Mishra

Example-01..
• If borrowed bit = 0, then it represents the first subnet.
• If borrowed bit = 1, then it represents the second subnet.
IP Address of the two subnets are-
• 200.1.2.00000000 = 200.1.2.0
• 200.1.2.10000000 = 200.1.2.128
6th
Sem
CSE
-
Internetworking
With
TCP/IP

For 1st Subnet-
• IP Address of the subnet = 200.1.2.0
• Total number of IP Addresses = 27 = 128
• Total number of hosts that can be configured = 128 – 2 = 126
• Range of IP Addresses = [200.1.2.00000000, 200.1.2.01111111] =
[200.1.2.0, 200.1.2.127]
• Direct Broadcast Address = 200.1.2.01111111 = 200.1.2.127
• Limited Broadcast Address = 255.255.255.255
6th
Sem
CSE
-
Internetworking
With
TCP/IP

For 2nd Subnet-
• IP Address of the subnet = 200.1.2.128
• Total number of IP Addresses = 27 = 128
• Total number of hosts that can be configured = 128 – 2 = 126
• Range of IP Addresses = [200.1.2.10000000, 200.1.2.11111111] =
[200.1.2.128, 200.1.2.255]
• Direct Broadcast Address = 200.1.2.11111111 = 200.1.2.255
• Limited Broadcast Address = 255.255.255.255
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Practice Example #1C: 255.255.255.128 (/25)
Network 192.168.10.0
 How many subnets? Since 128 is 1 bit on (10000000),
- The answer would be 21= 2.
 How many hosts per subnet?
- We have 7 host bits off (10000000), so the equation would be 27– 2 = 126 hosts.
 What are the valid subnets?
- 256 – 128 = 128. Remember, we’ll start at zero and count in our block size, so our
subnets are 0, 128.
 What’s the broadcast address for each subnet?
-The number right before the value of the next subnet is all host bits turned on and equals
the broadcast address. For the zero subnet, the next subnet is 128, so the broadcast of the 0
subnet is 127.
 What are the valid hosts?
-These are the numbers between the subnet and broadcast address
171
IP
Subnetting
&
Supernetting
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Prof.
D.
P.
Mishra

Logical Network Implementation
192.168.10.0 192.168.10.128
.129
.1
.2 .3 .130 .131
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IP
Subnetting
&
Supernetting
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Prof.
D.
P.
Mishra

Network 192.168.10.0
 How many subnets? 224 is 11100000, so our equation would be 23 = 8.
 How many hosts? 25– 2 = 30.
 What are the valid subnets? 256 – 224 = 32. We just start at zero and count to the
subnet mask value in blocks (increments) of 32: 0, 32, 64, 96, 128, 160, 192, and
224.
 What’s the broadcast address for each subnet (always the number right before the
next subnet)?
 What are the valid hosts (the numbers between the subnet number and the
broadcast address)?
173
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Subnetting
&
Supernetting
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Prof.
D.
P.
Mishra

Network 192.168.10.0
Subnet
Address
0 32 …………. 192 224
First Host 1 33 193 225
Last Host 30 62 222 254
Broadcast
Address
31 63 223 255
174
IP
Subnetting
&
Supernetting
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Prof.
D.
P.
Mishra

Practice Example #1B: 255.255.128.0 (/17)
Network 172.16.0.0
 Subnets? 21 = 2
 Hosts? 215– 2 = 32,766 (7 bits in the third octet, and 8 in the fourth)
 Valid subnets? 256 – 128 = 128. 0, 128. Remember that subnetting
is performed in the third octet, so the subnet numbers are really 0.0
and 128.0, as shown in the next table
 Broadcast address for each subnet?
 Valid hosts?
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Subnetting
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Supernetting
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D.
P.
Mishra

Network 172.16.0.0
Subnet 0.0 128.0
First Host 0.1 128.1
Last Host 127.254 255.254
Broadcast 127.255 255.255
176
IP
Subnetting
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Supernetting
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D.
P.
Mishra

Network 172.16.0.0
• Subnets? 24= 16.
• Hosts? 212 – 2 = 4094.
• Valid subnets? 256 – 240 = 0, 16, 32, 48, etc., up to 240.
• Broadcast address for each subnet?
• Valid hosts?
177
IP
Subnetting
&
Supernetting
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Prof.
D.
P.
Mishra

Practice Example #2B: 255.255.240.0 (/20) Network
172.16.0.0
Subnet 0.0 16.0 ……….. 240.0
First Host 0.1 16.1 240.1
Last Host 15.254 31.254 255.254
Broadcast 15.255 31.255 255.255
178
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Subnetting
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Supernetting
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D.
P.
Mishra

Ex-1
Suppose a network with IP Address 192.16.0.0. is divided into 2
subnets, find number of hosts per subnet.
• Also for the first subnet, find-
• Subnet Address
• First Host ID
• Last Host ID
• Broadcast Address
IP
Subnetting
&
Supernetting
-
Prof.
D.
P.
Mishra
179

Solution.
• Given IP Address belongs to class C.
• So, 24 bits are reserved for the Net ID.
• The given network is divided into 2 subnets.
• So, 1 bit is borrowed from the host ID part for the subnet IDs.
• Then, Number of bits remaining for the Host ID = 7.
• Thus, Number of hosts per subnet = 27 = 128.
IP
Subnetting
&
Supernetting
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Prof.
D.
P.
Mishra
180

Solution.
For 1st Subnet-
• Subnet Address = First IP Address = 192.16.0.00000000 =
192.16.0.0
• First Host ID = 192.16.0.00000001 = 192.16.0.1
• Last Host ID = 192.16.0.01111110 = 192.16.0.126
• Broadcast Address = Last IP Address = 192.16.0.01111111 =
192.16.0.127
IP
Subnetting
&
Supernetting
-
Prof.
D.
P.
Mishra
181

Ex-2
In a class B, network on the internet has a subnet mask of
255.255.240.0. What is the maximum number of hosts per subnet?
A. 4096
B. 4094
C. 4092
D. 4090
IP
Subnetting
&
Supernetting
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Prof.
D.
P.
Mishra
182

Solution.
• Number of bits reserved for network ID in the given subnet mask =
20.
• So, Number of bits reserved for Host ID = 32 – 20 = 12 bits.
• Thus, Number of hosts per subnet = 212 – 2 = 4094.
• In class B, 16 bits are reserved for the network.
• So, Number of bits reserved for subnet ID = 20 – 16 = 4 bits.
• Number of subnets possible = 24 = 16.
• Thus, Option (B) is correct.
IP
Subnetting
&
Supernetting
-
Prof.
D.
P.
Mishra
183

EX-3
What is not true about Subnetting?
A. It is applied for a single network
B. It is used to improve security
C. Bits are borrowed from network portion
D. Bits are borrowed from Host portion
IP
Subnetting
&
Supernetting
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Prof.
D.
P.
Mishra
184
Solution:
Option (C) is correct.

Supernetting
• Creating larger network
• Reverse process of Subnetting
• Combination of two or more networks
• Supernetting facilitates regional router aggregation
6th
Sem
CSE
-
Internetworking
With
TCP/IP

For Supernetting
• Need two or more Network or Subnets.
• Make the decimal network into binary value.
• Counting 0 and 1.
• Supernetting requires the use of routing protocols
• that support Classless Inter-Domain Routing (CIDR).
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Advantages of Supernet
• It reduces the size of routing updates.
• It provides a better overview of network.
• It decreases the use of resources such as Memory and CPU.
• It decreases the required time in rebuilding the routing tables.
6th
Sem
CSE
-
Internetworking
With
TCP/IP

Disadvantages of Supernetting
• The combination of blocks should be made in power 2;
• If three blocks are required, then there must be assigned four
blocks.
• The whole network should exist in the same class.
• When merged, it lacks covering different areas.
6th
Sem
CSE
-
Internetworking
With
TCP/IP

6th
Sem
CSE
-
Internetworking
With
TCP/IP
BASIS FOR COMPARISON SUBNETTING SUPERNETTING
Basic A process of dividing a network into
subnetworks.
A process of combining small
networks into a larger network.
Procedure The number of bits of network
addresses is increased.
The number of bits of host
addresses is increased.
Mask bits are moved towards Right of the default mask. Left of the default mask.
Implementation VLSM (Variable-length subnet
masking).
CIDR (Classless interdomain
routing).
Purpose Used to reduce the address depletion. To simplify and fasten the routing
process.

Conclusion
• Subnetting and supernetting both the terms have inverse meaning
• where Subnetting is used to separate the smaller subnetworks form
each other by dividing a larger network.
• Conversely, supernetting is used to combine the smaller range of
addresses into a larger one to make routing process more easy and
fast.
• Ultimately, both techniques are used to increase the availability
of the IP addresses and reduce the depletion of IP addresses.
6th
Sem
CSE
-
Internetworking
With
TCP/IP

IPSEC
6th
Sem
CSE
-
TCP/IP
(IPSEC-
IP
Security)
Fig: Security at Internet Layer as well as on upper layers too

Conceptual IPSEC Positioning
6th
Sem
CSE
-
TCP/IP
(IPSEC-
IP
Security)

IPSEC Services
6th
Sem
CSE
-
TCP/IP
(IPSEC-
IP
Security)

IPSEC HEADERS
6th
Sem
CSE
-
TCP/IP
(IPSEC-
IP
Security)

Modes of operation
6th
Sem
CSE
-
TCP/IP
(IPSEC-
IP
Security)

Tunnel Mode
6th
Sem
CSE
-
TCP/IP
(IPSEC-
IP
Security)

Tunnel Mode
Fig: Shows IPSEC in Tunnel Mode
6th
Sem
CSE
-
TCP/IP
(IPSEC-
IP
Security)

Transport Mode
Fig: Shows IPSEC in Transport Mode
Doesn’t hide Actual Source and Destination
Details
6th
Sem
CSE
-
TCP/IP
(IPSEC-
IP
Security)

IKE (Internet Key Exchange)
Supporting Protocol of IPSEC that
results SA
6th
Sem
CSE
-
TCP/IP
(IPSEC-
IP
Security)

Security Association (SA):
• SA is agreement between communicating parties about factors such as
• IPSEC protocol version in use
• Mode of operation (Transport or Tunnel mode)
• Cryptographic algorithm
• Cryptographic keys and lifetime of keys etc
• Once SA is established both major protocols IPSEC (i.e. AH and ESP)
make use of it for actual operation
• Note: If both AH and ESP are used in that case communicating parties
require two set of SA one for AH and other for ESP
6th
Sem
CSE
-
TCP/IP
(IPSEC-
IP
Security)

6th
Sem
CSE
-
TCP/IP
(IPSEC-
IP
Security)

• Connect two sites securely through public network
• Allow remote access by individual users.
• Allows travelling users to remotely access private network
• If we remove VPN link then two sites will be separated with each
other
• By employing VPN two remote sites seems to be the one/single virtual
site
What is VPN ?
6th
Sem
CSE
-
TCP/IP
(IPSEC-
IP
Security)

Architecture of VPN
6th
Sem
CSE
-
TCP/IP
(IPSEC-
IP
Security)

Working of VPN.
6th
Sem
CSE
-
TCP/IP
(IPSEC-
IP
Security)

Working of VPN..
6th
Sem
CSE
-
TCP/IP
(IPSEC-
IP
Security)

Types of VPN
• Remote access VPN
• Intranet VPN
• Extranet VPN
6th
Sem
CSE
-
TCP/IP
(IPSEC-
IP
Security)

Remote Access VPN
• Gives access to remote or roaming users access of Main office / branch
office as shown in above block diagram
6th
Sem
CSE
-
TCP/IP
(IPSEC-
IP
Security)

Intranet VPN
• As shown in above block diagram Intranet VPN is used for joining
different branches of same organization.
6th
Sem
CSE
-
TCP/IP
(IPSEC-
IP
Security)

Extranet VPN
• As shown main branch office is connected to different business partners through
VPN, as Extranet VPN joins branch offices as well the business partners too i.e.
it’s not compulsion to provide VPN service to client branch offices only
6th
Sem
CSE
-
TCP/IP
(IPSEC-
IP
Security)

Advantages of VPN
• Greater scalability
• Easy to add or remove users
• Reduce long distance Telecommunication cost
• Mobility
• Scalability
6th
Sem
CSE
-
TCP/IP
(IPSEC-
IP
Security)

Disadvantages of VPN
• Lack of standards
• Understanding of security issues
• Unpredictable Intranet traffic
• Difficult to accommodate product from different vendors
6th
Sem
CSE
-
TCP/IP
(IPSEC-
IP
Security)

• The wonder of IPv6 lies in its header.
• An IPv6 address is 4 times larger than IPv4, but surprisingly,
• the header of an IPv6 address is only 2 times larger than IPv4.
• IPv6 headers have one Fixed Header and zero or more Optional
(Extension) Headers.
• All the necessary information that is essential for a router is kept in
the Fixed Header.
• The Extension Header contains optional information that helps
routers to understand how to handle a packet/flow.
6th
Sem
CSE
-
TCP/IP
(IPSEC-
IP
Security)
IPv6 – Header.

IPv6 – Header..
6th
Sem
CSE
-
TCP/IP
(IPSEC-
IP
Security)

6th
Sem
CSE
-
TCP/IP
(IPSEC-
IP
Security)
S.N. Field & Description
1 Version (4-bits): It represents the version of Internet Protocol, i.e. 0110.
2
Traffic Class (8-bits): These 8 bits are divided into two parts.
The most significant 6 bits are used for Type of Service to let the Router Known what services should be provided to this
packet. The least significant 2 bits are used for Explicit Congestion Notification (ECN).
3
Flow Label (20-bits): This label is used to maintain the sequential flow of the packets belonging to a communication.
The source labels the sequence to help the router identify that a particular packet belongs to a specific flow of information.
This field helps avoid re-ordering of data packets. It is designed for streaming/real-time media.
4
Payload Length (16-bits): This field is used to tell the routers how much information a particular packet contains in its
payload. Payload is composed of Extension Headers and Upper Layer data. With 16 bits, up to 65535 bytes can be indicated;
but if the Extension Headers contain Hop-by-Hop Extension Header, then the payload may exceed 65535 bytes and this field is
set to 0.
5
Next Header (8-bits): This field is used to indicate either the type of Extension Header, or if the Extension Header is not
present then it indicates the Upper Layer PDU. The values for the type of Upper Layer PDU are same as IPv4’s.
6
Hop Limit (8-bits): This field is used to stop packet to loop in the network infinitely. This is same as TTL in IPv4. The value of
Hop Limit field is decremented by 1 as it passes a link (router/hop). When the field reaches 0 the packet is discarded.
7 Source Address (128-bits): This field indicates the address of originator of the packet.
8 Destination Address (128-bits): This field provides the address of intended recipient of the packet.

Difference between IPv4 and IPv6
6th
Sem
CSE
-
TCP/IP
(IPSEC-
IP
Security)

6th
Sem
CSE
-
TCP/IP
(IPSEC-
IP
Security)
BASIS OF COMPARISON IPV4 IPV6
Address Configuration
Supports Manual and DHCP
configuration.
Supports Auto-configuration and
renumbering
End-to-end connection integrity Unachievable Achievable
Address Space It can generate 4.29 x 109 addresses.
It can produce quite a large number of
addresses, i.e., 3.4 x 1038.
Security features Security is dependent on application IPSEC is inbuilt in the IPv6 protocol
Address length 32 bits (4 bytes) 128 bits (16 bytes)
Address Representation In decimal In hexadecimal
Fragmentation performed by Sender and forwarding routers Only by the sender
Packet flow identification Not available
Available and uses flow label field in
the header
Checksum Field
Available Not available
Message Transmission Scheme
Broadcasting Multicasting and Any casting
Encryption and Authentication
Not Provided Provided

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