Chapter 4 of the document discusses the network layer of the OSI model, which facilitates end-to-end logical addressing for data routing across various networks. It outlines the functions of the network layer, including logical addressing, routing, and packet encapsulation, while describing switching techniques such as circuit, message, and packet switching. Additionally, the chapter explains routing algorithms, router functions, and the different types and metrics used in routing protocols.

1. COMPUTER NETWORKS
USHA BARAD
Assistant Professor

2. CHAPTER 4

3. Outlines
• Introduction
• Virtual and Datagram networks
• Study of router
• IP protocol and addressing in the Internet
• Routing algorithms
• Broadcast and Multicast routing

4. Introduction
 Layer 3, the network layer of the OSI model, provides an end-to-end
logical addressing system so that a packet of data can be routed across
several layer 2 networks (Ethernet, Token Ring, Frame Relay, etc.).
Note that network layer addresses can also be referred to as logical
addresses.

6. • The third-lowest layer of the OSI Reference Model is
the network layer.
• If the data link layer is the one that basically defines the
boundaries of what is considered a network, the
network layer is the one that defines
how internetworks (interconnected networks) function.
• The network layer is the lowest one in the OSI model
that is concerned with actually getting data from one
computer to another even if it is on a remote network;
in contrast, the data link layer only deals with devices
that are local to each other.
• Network layer functions are explain below:

7. • Logical Addressing:
– Every device that communicates over a network has associated
with it a logical address, sometimes called a layer three address.
– For example, on the Internet, the Internet Protocol (IP) is the
network layer protocol and every machine has an IP address.
– Note that addressing is done at the data link layer as well, but
those addresses refer to local physical devices.
– In contrast, logical addresses are independent of particular
hardware and must be unique across an entire internetwork.
• Routing:
– Moving data across a series of interconnected networks is
probably the defining function of the network layer.
– It is the job of the devices and software routines that function at
the network layer to handle incoming packets from various
sources, determine their final destination, and then figure out
where they need to be sent to get them where they are supposed
to go.

8. • Datagram Encapsulation:
– The network layer normally encapsulates messages received from higher
layers by placing them into datagrams (also called packets) with a network
layer header.
• Fragmentation and Reassembly:
– The network layer must send messages down to the data link layer for
transmission.
– Some data link layer technologies have limits on the length of any message
that can be sent.
– If the packet that the network layer wants to send is too large, the
network layer must split the packet up, send each piece to the data link
layer, and then have pieces reassembled once they arrive at the network
layer on the destination machine.
– A good example is how this is done by the Internet Protocol.
• Error Handling and Diagnostics:
– Special protocols are used at the network layer to allow devices that are
logically connected, or that are trying to route traffic, to exchange
information about the status of hosts on the network or the devices
themselves.

9. Network Layer Design Goals
1. The services provided by the network layer
should be independent of the subnet topology.
2. The Transport Layer should be shielded from
the number, type and topology of the subnets
present.
3. The network addresses available to the
Transport Layer should use a uniform
numbering plan (even across LANs and WANs).

11. Network Layer – supervises host-to-host packet delivery – hosts
could be separated by several physical networks
data-link layer provides node-to-node delivery,
transport layer provides process-to-process delivery

12. Major (Basic) Network Layer Duties
• Addressing : identify each device uniquely to
allow global communication
• Routing : determine optimal route for sending
a packet from one host to another
• Packetizing: encapsulate packets received
from upper-layer protocols
• Fragmenting : decapsulate packets from one
and encapsulate them for another network

13. Issues at the Network Layer
• Switching Technique:
– Datagrams
– Virtual circuits
• Routing:
– How to forward packets
– How to calculate a path from source to destination?
• Traffic Control:
– Congestion control
– Rate control

14. Network service model

16. Network layer connection and
connection-less service
• Datagram network provides network-layer
connectionless service
• VC network provides network-layer
connection service
• Analogous to the transport-layer services,
but:
❍ Service: host-to-host
❍ No choice: network provides one or the other
❍ Implementation: in the core

17. Connectionless Service
• Each packet is transmitted independently

18. Connection-oriented Service
• Logical connection is established

19. Switching Techniques
• In large networks there might be multiple
paths linking sender and receiver.
• Information may be switched as it travels
through various communication channels.
• There are three typical switching techniques
available for digital traffic.
• Circuit Switching
• Message Switching
• Packet Switching

20. Circuit Switching
• Circuit switching is a technique that directly connects
the sender and the receiver in an unbroken path.
• Telephone switching equipment, for example,
establishes a path that connects the caller's telephone
to the receiver's telephone by making a physical
connection.
• With this type of switching technique, once a
connection is established, a dedicated path exists
between both ends until the connection is terminated.
• Routing decisions must be made when the circuit is first
established, but there are no decisions made after that
time.

21. Circuit Switching
• Circuit switching in a network operates almost the
same way as the telephone system works.
• A complete end-to-end path must exist before
communication can take place.
• The computer initiating the data transfer must ask
for a connection to the destination.
• Once the connection has been initiated and
completed to the destination device, the destination
device must acknowledge that it is ready and willing
to carry on a transfer.

22. Circuit switching
• Advantages:
• The communication channel (once established) is dedicated.
• Disadvantages:
• Possible long wait to establish a connection, (10 seconds,
more on long- distance or international calls.) during which
no data can be transmitted.
• More expensive than any other switching techniques,
because a dedicated path is required for each connection.
• Inefficient use of the communication channel, because the
channel is not used when the connected systems are not
using it.

23. Message Switching
• With message switching there is no need to establish
a dedicated path between two stations.
• When a station sends a message, the destination
address is appended to the message.
• The message is then transmitted through the
network, in its entirety, from node to node.
• Each node receives the entire message, stores it in its
entirety on disk, and then transmits the message to
the next node.
• This type of network is called a store-and-forward
network.

24. Message Switching
• A message-switching node is typically a general-purpose
computer.
• The device needs sufficient secondary-storage capacity to store
the incoming messages, which could be long.
• A time delay is introduced using this type of scheme due to
store- and-forward time, plus the time required to find the next
node in the transmission path.

25. Message Switching
• Advantages:
• Channel efficiency can be greater compared to circuit-
switched systems, because more devices are sharing the
channel.
• Traffic congestion can be reduced, because messages may
be temporarily stored in route.
• Message priorities can be established due to store-and-
forward technique.
• Message broadcasting can be achieved with the use of
broadcast address appended in the message.

26. Message Switching
• Disadvantages
• Message switching is not compatible with
interactive applications.
• Store-and-forward devices are expensive, because
they must have large disks to hold potentially long
messages.

27. Packet Switching
• Packet switching can be seen as a solution that tries to combine the
advantages of message and circuit switching and to minimize the
disadvantages of both.
• There are two methods of packet switching: Datagram and
virtual circuit.

28. Packet Switching
• In both packet switching methods, a message is broken into
small parts, called packets.
• Each packet is tagged with appropriate source and destination
addresses.
• Since packets have a strictly defined maximum length, they can be
stored in main memory instead of disk, therefore access delay and
cost are minimized.
• Also the transmission speeds, between nodes, are optimized.
• With current technology, packets are generally accepted onto the
network on a first-come, first-served basis. If the network becomes
overloaded, packets are delayed or discarded (``dropped'').

29. Packet size
• The size of the packet can vary from 180 bits, the
size for the Datakit® virtual circuit switch designed
by Bell Labs for communications and business
applications; to 1,024 or 2,048 bits for the 1PSS®
switch, also designed by Bell Labs for public data
networking; to 53 bytes for ATM switching, such as
Lucent Technologies' packet switches.

30. Packet switching
• In packet switching, the analog signal from your phone
is converted into a digital data stream.
• That series of digital bits is then divided into relatively
tiny clusters of bits, called packets.
• Each packet has at its beginning the digital address -- a
long number -- to which it is being sent.
• The system blasts out all those tiny packets, as fast as it
can, and they travel across the nation's digital backbone
systems to their destination: the telephone, or rather the
telephone system, of the person you're calling.

31. Packet switching
• They do not necessarily travel together; they
do not travel sequentially.
• They don't even all travel via the same route.
• But eventually they arrive at the right point --
that digital address added to the front of each
string of digital data -- and at their destination
are reassembled into the correct order, then
converted to analog form, so your friend can
understand what you're saying.

32. Packet Switching: Datagram
• Datagram packet switching is similar to message
switching in that each packet is a self-contained unit with
complete addressing information attached.
• This fact allows packets to take a variety of possible paths
through the network.
• So the packets, each with the same destination address, do
not follow the same route, and they may arrive out of
sequence at the exit point node (or the destination).
• Reordering is done at the destination point based on the
sequence number of the packets.
• It is possible for a packet to be destroyed if one of the
nodes on its way is crashed momentarily. Thus all its
queued packets may be lost.

33. Each packet is routed independently

34. Datagram networks

35. Packet Switching:Virtual Circuit
• In the virtual circuit approach, a preplanned route is established
before any data packets are sent.
• A logical connection is established when
 a sender send a "call request packet" to the receiver and
 the receiver send back an acknowledge packet "call accepted
packet" to the sender if the receiver agrees on conversational
parameters.
• The conversational parameters can be maximum packet sizes, path
to be taken, and other variables necessary to establish and maintain
the conversation.
• Virtual circuits imply acknowledgements, flow control, and error
control, so virtual circuits are reliable.
• That is, they have the capability to inform upper-protocol layers if a
transmission problem occurs.

36. Packet Switching:Virtual Circuit
• In virtual circuit, the route between stations does not mean that
this is a dedicated path, as in circuit switching.
• A packet is still buffered at each node and queued for output over a
line.
• The difference between virtual circuit and datagram approaches:
 With virtual circuit, the node does not need to make a routing
decision for each packet.
 It is made only once for all packets using that virtual circuit.

37. Packet Switching: Virtual Circuit
VC's offer guarantees that
 the packets sent arrive in the order sent
 with no duplicates or omissions
 with no errors (with high probability) regardless of how
they are implemented internally.

39. VC implementation

40. Forwarding table

41. Virtual circuits: signaling protocols

44. Advantages of packet switching
Advantages:
• Packet switching is cost effective, because switching devices
do not need massive amount of secondary storage.
• Packet switching offers improved delay characteristics, because
there are no long messages in the queue (maximum packet size is
fixed).
• Packet can be rerouted if there is any problem, such as, busy or
disabled links.
• The advantage of packet switching is that many network users
can share the same channel at the same time. Packet switching
can maximize link efficiency by making optimal use of link
bandwidth.

45. Disadvantages of packet switching
Disadvantages:
• Protocols for packet switching are typically more complex.
• It can add some initial costs in implementation.
• If packet is lost, sender needs to retransmit the data.
• Another disadvantage is that packet-switched systems still can’t
deliver the same quality as dedicated circuits in applications
requiring very little delay - like voice conversations or moving
images.

46. Comparison of Datagram and
Virtual Circuit

47. Study of router
• A router is a device that forwards data packets along
networks.
• Routing is the act of moving information across an inter-
network from a source to a destination.
• A router is connected to at least two networks, commonly two
LANs or WANs or a LAN and its ISP's network.
• Routers are located at gateways, the places where two or
more networks connect.

48. Routers
• Special type of computer
• Connect and allow communication between
two networks
• Determine the best path through the network
• Configuration files to control the traffic
• Generally have two connection types:
– WAN connection (connection to ISP)
– LAN connection

50. Router components
• CPU
– Executes operation systems instructions
• RAM
– Stores instructions and data needed for CPU
• ROM
– Boot instructions, scaled-down vers. of IOS
• Flash
– Stores IOS, copied into RAM during bootup proc.
• NVRAM
– Startup configuration file

52. • Desirable properties of a router are as follows:
• Correctness and simplicity: The packets are to be
correctly delivered. Simpler the routing algorithm, it is
better.
• Robustness: Ability of the network to deliver packets via
some route even in the face of failures.
• Stability: The algorithm should converge to equilibrium
fast in the face of changing conditions in the network.
• Fairness and optimality: obvious requirements, but
conflicting.
• Efficiency: Minimum overhead

53. • While designing a routing protocol it is necessary to take
into account the following design parameters:
• Performance Criteria: Number of hops, Cost, Delay,
Throughput, etc
• Decision Time: Per packet basis (Datagram) or per
session (Virtual-circuit) basis
• Decision Place: Each node (distributed), Central node
(centralized), Originated node (source)
• Network Information Source: None, Local, Adjacent
node, Nodes along route, All nodes
• Network Information Update Timing: Continuous,
Periodic, Major load change, Topology change

54. Classification of Routers
• Routing algorithms can be classified based on the
following criteria:
– Static versus Adaptive
– Single-path versus multi-path
– Intra-domain versus inter-domain
– Flat versus hierarchical
– Link-state versus distance vector
– Host-intelligent versus router-intelligent

55. Static versus Adaptive
• This category is based on how and when the routing tables are
set-up and how they can be modified, if at all.
• Adaptive routing is also referred as dynamic routing and Non-
adaptive is also known as static routing algorithms.
• Static routing algorithms are hardly algorithms at all; the table
mappings are established by the network administrator before
the beginning of routing.
• Most of the dominant routing algorithms today are dynamic
routing algorithms, which adjust to changing network
circumstances by analyzing incoming routing update messages.
• If the message indicates that a network change has occurred,
the routing software recalculates routes and sends out new
routing update messages.

56. Single-Path versus Multi-path
• This division is based upon the number of paths a router
stores for a single destination.
• Single path algorithms are where only a single path (or
rather single next hop) is stored in the routing table.
• Some sophisticated routing protocols support multiple
paths to the same destination; these are known as multi-
path algorithms.
• Unlike single-path algorithms, these multipath
algorithms permit traffic multiplexing over multiple lines.
• The advantages of multipath algorithms are obvious:
They can provide substantially better throughput and
reliability. This is generally called load sharing.

57. Intradomain versus Interdomain
• Some routing algorithms work only within
domains; others work within and between
domains.
• The nature of these two algorithm types is
different.
• It stands to reason, therefore, that an optimal
intra-domain-routing algorithm would not
necessarily be an optimal inter-domain-
routing algorithm.

58. Flat Versus Hierarchical
• Some routing algorithms operate in a flat space, while
others use routing hierarchies.
• In a flat routing system, the routers are peers of all
others.
• In a hierarchical routing system, some routers form what
amounts to a routing backbone.
• Packets from non-backbone routers travel to the
backbone routers, where they are sent through the
backbone until they reach the general area of the
destination.
• “A backbone router is a type of router that links
separate systems in different meshes of a network with
each other. As its name suggests, a backbone
router plays the role of a backbone in any network

59. Link-State versus Distance Vector
• This category is based on the way the routing tables are
updated.
– Distance vector algorithms (also known as Bellman-Ford
algorithms): Key features of the distance vector routing are as
follows:
– The routers share the knowledge of the entire autonomous
system
– Sharing of information takes place only with the neighbors
– Sharing of information takes place at fixed regular intervals, say
every 30 seconds.

60. • Link-state algorithms (also known as shortest path first
algorithms) have the following key feature.
• The routers share the knowledge only about their
neighbors compared to all the routers in the
autonomous system.
• Sharing of information takes place only with all the
routers in the internet, by sending small updates using
flooding compared to sending larger updates to their
neighbors.
• Sharing of information takes place only when there is a
change, which leads to lesser internet traffic compared
to distance vector routing.

61. Host-Intelligent Versus Router-
Intelligent
• This division is on the basis of whether the source
knows about the entire route or just about the next-
hop where to forward the packet.
• Some routing algorithms assume that the source end
node will determine the entire route.
• This is usually referred to as source routing.
• In source-routing systems, routers merely act as
store-and-forward devices, mindlessly sending the
packet to the next stop.
• These algorithms are also referred to as Host-
Intelligent Routing, as entire route is specified by the
source node.

62. Routing Algorithm Metrics
• Routing tables contain information used by switching
software to select the best route.
• Routing algorithms have used many different metrics to
determine the best route.
• Sophisticated routing algorithms can base route selection on
multiple metrics, combining them in a single (hybrid) metric.
• All the following metrics have been used:
– Path length
– Delay
– Bandwidth
– Load
– Communication cost
– Reliability

63. • Path length is the most common routing metric.
• Some routing protocols allow network administrators to assign
arbitrary costs to each network link.
• In this case, path length is the sum of the costs associated with
each link traversed.
• Other routing protocols define hop count, a metric that specifies
the number of passes through internetworking products, such as
routers, that a packet must pass through in a route from a source
to a destination.
• Routing delay refers to the length of time required to move a
packet from source to destination through the internet.
• Bandwidth refers to the available traffic capacity of a link.
• All other things being equal, a 10-Mbps Ethernet link would be
preferable to a 64-kbps leased line.

64. • Load refers to the degree to which a network resource,
such as a router, is busy.
• Load can be calculated in a variety of ways, including CPU
utilization and packets processed per second.
• Communication cost is another important metric,
especially because some companies may not care about
performance as much as they care about operating
expenditures.
• Reliability, in the context of routing algorithms, refers
to the dependability (usually described in terms of the
bit-error rate) of each network link.
• Some network links might go down more often than
others.

65. Static Routing
• Configured manually
• Specifies network address and subnet mask of
remote network, and IP address of next hop router
or exit interface
• Use static routes when:
– Network only consists of few routers
– Network is connected to Internet only through one
ISP
• Advantages:
– Minimal CPU processing
– Easy to configure
– Easier for administrator to understand

66. • Disadvantages:
• Configuration and maintenance is time
consuming
• Does not scale well with growing networks
• Requires complete knowledge of the whole
network for proper implementation

68. Dynamic routing
• Added to routing table by using a dynamic
routing protocol
• Used by routers to share information about
the reachability and status of remote
networks
• Perform several activities:
– Network discovery
– Updating and maintaining routing tables

69. • Advantages:
• Less administrative overhead when adding or
deleting a network
• Protocols automatically react to the topology
changes
• More scalable
• Disadvantages:
• Router resources are used (CPU cycles, memory
and link bandwidth)
• More administrator knowledge is required for
configuration, verification and troubleshooting

74. Internet Router Architecture
• Router
• 3-layer (physical, data-link, network) device,
with 3 key functions:
– run routing algorithms/protocols (RIP, OSPF, BGP)
– forward/switch IP packets from incoming to
proper outgoing links
– manage congestion

76. Example [ forwarding / routing table ]

80. IP protocol and addressing in the
Internet
• The Internet Protocol (IP) is the method
or protocol by which data is sent from one
computer to another on the Internet.
• Each computer (known as a host) on the
Internet has at least one IP address that
uniquely identifies it from all other computers
on the Internet.

81. • The Internet protocols are the world’s most popular
open-system (nonproprietary) protocol suite because
they can be used to communicate across any set of
interconnected networks and are equally well suited for
LAN and WAN communications.
• The Internet protocols consist of a suite of
communication protocols, of which the two best known
are the Transmission Control Protocol (TCP) and the
Internet Protocol (IP).
• The Internet protocol suite not only includes lower-layer
protocols (such as TCP and IP), but it also specifies
common applications such as electronic mail, terminal
emulation, and file transfer

83. Internet Protocol (IP)
• The Internet Protocol (IP) is a network-layer (Layer 3)
protocol that contains addressing information and some
control information that enables packets to be routed.
• IP is documented in RFC 791 and is the primary network-
layer protocol in the Internet protocol suite.
• Along with the Transmission Control Protocol (TCP), IP
represents the heart of the Internet protocols.
• IP has two primary responsibilities: providing
connectionless, best-effort delivery of datagrams through
an internetwork; and providing fragmentation and
reassembly of datagrams to support data links with
different maximum-transmission unit (MTU) sizes.

84. Continue…
• Provides addressing of sender and receiver on
the internet
• Protocol defines how to route messages
through a network
– Packetized
– Not continuous
– Delivery not guaranteed
• Dealt with at every router on the way from
sender to receiver

85. IP Packet Format

86. IP Routing

87. Network layer protocols
• Routing Protocols
– BGP (BGP-4): Border Gateway Protocol
– EGP: Exterior Gateway Protocol
– IP: Internet Protocol (IPv4)
– IPv6: Internet Protocol version 6
– ICMP & ICMPv6: Internet Message Control Protocol and ICMP
version 6
– IRDP: ICMP Router Discovery Protocol
– Mobile IP: IP Mobility Support Protocol for IPv4 & IPv6
– NARP: NBMA Address Resolution Protocol
– NHRP: Next Hop Resolution Protocol
– OSPF: Open Shortest Path Firest Protocol (version 2)
– RIP: Routing Information Protocol (RIP2)
– RSVP: Resource ReSerVation Protocol
–

88. • Multicasting Protocols
– BGMP: Border Gateway Multicast Protocol
– DVMRP: Distance Vector Multicast Routing Protocol
– IGMP : Internet Group Management Protocol
– MARS: Multicast Address Resolution Server
– MBGP: Multiprotocol BGP
– MOSPF: Multicast Extensions to OSPF
– MSDP: Multicast Source Discovery Protocol
– MZAP: Multicast-Scope Zone Anncuncement Protocol
– PGM: Pragmatic General Multicast Protocol
– PIM-DM: Protocol Independent Multicast - Dense Mode
– PIM-SM: Protocol Independent Multicast - Sparse
Mode

89. • MPLS Protocols
– MPLS: Multiprotocol Label Switching
– CR-LDP: Constraint-based LDP
– LDP: Label Distribution Protocol
– RSVP-TE: Resource Reservation Protocol - Traffic
Extension
• Data Link Layer Protocols
– ARP and InARP: Address Resolution Protocol and
Inverse ARP
– IPCP and IPv6CP: IP Control Protocol and IPv6 Control
Protocol
– RARP: Reverse Address Resolution Protocol
– SLIP: Serial Line IP

90. DHCP: Dynamic Host Configuration
Protocol-Dec 2010
• Dynamic Host Configuration Protocol (DHCP) is a
communications protocol enabling network
administrators manage centrally and to automate the
assignment of IP addresses in a network.
• In an IP network, each device connecting to the Internet
needs a unique IP address.
• DHCP lets a network administrator supervise and
distribute IP addresses from a central point and
automatically sends a new IP address when a computer
is plugged into a different place in the network.

91. • DHCP uses the concept of a “lease” or amount of time
that a given IP address will be valid for a computer.
• The lease time can vary depending on how long a user is
likely to require the Internet connection at a particular
location.
• It’s especially useful in education and other
environments where users change frequently.
• Using very short leases, DHCP can dynamically recon-
figure networks in which there are more computers than
there are available IP addresses.
• DHCP supports static addresses for computers
containing Web servers that need a permanent IP
address.

92. • DHCP is an alternative to another network IP
management protocol, Bootstrap Protocol (BOOTP).
• DHCP is a more advanced protocol but both
configuration management protocols are commonly
used.
• A DHCP or BOOTP client is a program that is located in
each computer so that it can be configured.

94. • Op The message operation code.
– Messages can be either BOOTREQUEST or BOOTREPLY.
• Htype The hardware address type.
• Hlen The hardware address length.
• Xid The transaction ID.
• Secs The seconds elapsed since the client began the
address acquisition or renewal process.
• Flags The flags.
• Ciaddr The client IP address.
• Yiaddr The “Your” (client) IP address.
• Siaddr The IP address of the next server to use in
bootstrap.

95. • Giaddr The relay agent IP address used in booting
via a relay agent.
• Chaddr The client hardware address.
• Sname Optional server host name, null
terminated string
• File Boot file name, null terminated string;
generic name or null in DHCPDISCOVER, fully
qualified directory-path name in DHCPOFFER.
• Options Optional parameters field. See the
options documents for a list of defined options.

96. IP: Internet Protocol (IPv4)
• The Internet Protocol (IP) is a network-layer (Layer 3 in the OSI
model) protocol that contains addressing information and some
control information to enable packets to be routed in a network.
• IP is the primary network-layer protocol in the TCP/IP protocol
suite.
• Along with the Transmission Control Protocol (TCP), IP represents
the heart of the Internet protocols.
• IP has two primary responsibilities: providing connectionless, best-
effort delivery of datagrams through a network; and providing
fragmentation and reassembly of datagrams to support data links
with different maximum-transmission unit (MTU) sizes.
• The IP addressing scheme is integral to the process of routing IP
datagrams through an internetwork.

98. • Version— 4-bit field indicates the version of IP currently
used.
• IP Header Length (IHL)— is the datagram header length
in 32-bit words.
• Type-of-Service— indicates the quality of service
desired by specifying how an upper-layer protocol
would like a current datagram to be handled, and
assigns datagrams various levels of importance.
• Total Length—specifies the length, in bytes, of the
entire IP packet, including the data and header.
• Identification—contains an integer that identifies the
current datagram.
• Flags—consists of a 3-bit field of which the two low
order (least-significant) bits control fragmentation.

99. • Fragment Offset— This 13-bits field indicates the position of
the fragment’s data relative to the beginning of the data in
the original datagram, which allows the destination IP
process to properly reconstruct the original datagram.
• Time-to-Live— is a counter that gradually decrements down
to zero, at which point the datagram is discarded.
• Protocol—indicates which upper-layer protocol receives
incoming packets after IP processing is complete.
• Header Checksum—helps ensure IP header integrity.
• Source Address—specifies the sending node.
• Destination Address—specifies the receiving node.
• Options—allows IP to support various options, such as
security.
• Data—contains upper-layer information.

100. IPv6: Internet Protocol version 6
• IPv6 is the new version of Internet Protocol (IP) based on IPv4, a
network-layer (Layer 3) protocol that contains addressing
information and some control information enabling packets to be
routed in the network.
• There are two basic IP versions: IPv4 and IPv6. IPv6 is also called
next generation IP or IPng.
• IPv4 and IPv6 are de-multiplexed at the media layer.
• IPv6 increases the IP address size from 32 bits to 128 bits, to
support more levels of addressing hierarchy, a much greater
number of addressable nodes and simpler auto-configuration of
addresses.
• IPv6 addresses are expressed in hexadecimal format (base 16)
which allows not only numerals (0-9) but a few characters as well
(a-f).

102. • Version – 4-bit Internet Protocol Version number (IPv6 is 6).Priority
-- 8-bit traffic class field enables a source to identify the desired
delivery priority of the packets.
• Flow label -- 20-bit flow label is used by a source to label those
products for which it requests special handling by the IPv6 router.
• Payload length -- 16-bit integer in octets is the length of payload
including header.
• Next header – 8-bit selector identifies the type of header
immediately following the IPv6 header.
• Hop limit -- 8-bit integer that is decremented by one by each node
that forwards the packet. The packet is discarded if the Hop Limit
is decremented to zero.
• Source address -- 128-bit address of the originator of the packet .
• Destination address -- 128-bit address of the intended recipient of
the packet (possibly not the ultimate recipient, if a Routing header
is present).

103. Border Gateway Protocol (BGP)
• Border Gateway Protocol (BGP) is a
standardized exterior gateway protocol designed
to exchange routing and reachability information
among autonomous systems (AS) on the
Internet.
• The protocol is often classified as a path
vector protocol but is sometimes also classed as
a distance-vector routing protocol.

104. • BGP is the only protocol that is designed to deal with a
network of the Internet’s size, and the only protocol
that can deal well with having multiple connections to
unrelated routing domains.

105. ICMP : Internet Message Control
Protocol
• Internet Control Message Protocol (ICMP) is an
integrated part of the IP suite.
• ICMP messages, delivered in IP packets, are used
for out-of-band messages related to network
operation or mis-operation.
• ICMP packet delivery is unreliable, so hosts can’t
count on receiving ICMP packets for any network
problems.

106. • The key ICMP functions are:
– Announce network errors
– Announce network congestion
– Assist Troubleshooting
– Announce Timeouts
• The Internet Control Message Protocol (ICMP)
was revised during the definition of IPv6.
• In addition, the multicast control functions of
the IPv4 Group Membership Protocol (IGMP) are
now incorporated in the ICMPv6.

107. • Type -- Messages can be error or informational messages.
• Code -- For each type of message several different codes
are defined.
• Checksum -- The 16-bit one’s complement of the one’s
complement sum of the ICMP message starting with the
ICMP Type.
• Identifier -- An identifier to aid in matching requests/ replies;
may be zero.
• Sequence number -- Sequence number to aid in matching
requests/replies; may be zero.
• Address mask -- A 32-bit mask.

108. OSPF: Open Shortest Path
First protocol
• Open Shortest Path First (OSPF) is an interior gateway
protocol which is used for routing between routers
belonging to a single Autonomous System.
• OSPF uses link-state technology in which routers send each
other information about the direct connections and links
which they have to other routers.
• Each OSPF router maintains an identical database describing
the Autonomous System’s topology.
• From this database, a routing table is calculated by
constructing a shortest- path tree.
• OSPF recalculates routes quickly in the face of topological
changes, utilizing a minimum of routing protocol traffic.

109. Version number - Protocol version number (currently
2).
• Packet type - Valid types are as follows:
1 Hello
2 Database Description
3 Link State Request
4 Link State Update
5 Link State Acknowledgment.

110. • Packet length - The length of the protocol packet in bytes. This
length includes the standard OSPF header.
• Router ID - The router ID of the packet’s source. In OSPF, the
source and destination of a routing protocol packet are the two
ends of a (potential) adjacency.
• Area ID - identifying the area that this packet belongs to. All
OSPF packets are associated with a single area. Most travel a
single hop only.
• Checksum - The standard IP checksum of the entire contents of
the packet, starting with the OSPF packet header but excluding
the 64-bit authentication field.
• AuType - Identifies the authentication scheme to be used for
the packet.
• Authentication - A 64-bit field for use by the authentication
scheme.

111. RIP: Routing Information Protocol
(RIP2)
• Routing Information Protocol (RIP) is a standard for
exchange of routing information among gateways and
hosts.
• This protocol is most useful as an “interior gateway
protocol”.
• RIP2, derives from RIP, is an extension of the Routing
Information Protocol (RIP) intended to expand the
amount of useful information carried in the RIP2
messages and to add a measure of security.
• RIP2 is a UDP-based protocol.
• Each host that uses RIP2 has a routing process that
sends and receives datagrams on UDP port number 520.

112. • Command -- The command field is used to specify the purpose of the
datagram. There are five commands:
Request, Response, Traceon (obsolete),Traceoff (Obsolete) and Reserved.
•Version -- The RIP version number. The current version is 2.
•Address family identifier -- Indicates what type of address is specified in
this particular entry. This is used because RIP2 may carry routing
information for several
different protocols.
•Route tag -- Attribute assigned to a route which must be preserved and
readvertised with a route.

113. • IP address -- The destination IP address.
• Subnet mask -- Value applied to the IP address to yield
the non-host portion of the address. If zero, then no
subnet mask has been included for this entry.
• Next hop -- Immediate next hop IP address to which
packets to the destination specified by this route entry
should be forwarded.
• Metric -- Represents the total cost of getting a
datagram from the host to that destination. This metric
is the sum of the costs associated with the networks
that would be traversed in getting to the destination

114. Internet Protocol address
• Short for Internet Protocol address,
an IP or IP address is a number (example
shown right) used to indicate the location of a
computer or other device on a network
using TCP/IP.
• These addresses are similar to those of your
house; they allow data to reach the
appropriate destination on a network and the
Internet.

115. The Format of an IP Address
• The format of an IP address is a 32-bit numeric address
written as four numbers separated by periods. Each
number can be zero to 255.
• For example, 1.160.10.240 could be an IP address.
• Within an isolated network, you can assign IP addresses
at random as long as each one is unique.
• However, connecting a private network to the Internet
requires using registered IP addresses (called Internet
addresses) to avoid duplicates.

116. Static Versus Dynamic IP Addresses
• An IP address can be static or dynamic. A static IP
address will never change and it is a permanent Internet
address.
• A dynamic IP address is a temporary address that is
assigned each time a computer or device accesses the
Internet.
• The four numbers in an IP address are used in different
ways to identify a particular network and a host on that
network.
– Class A - supports 16 million hosts on each of 126 networks
– Class B - supports 65,000 hosts on each of 16,000 networks
– Class C - supports 254 hosts on each of 2 million networks

117. • There are five classes of available IP ranges:
• Class A, Class B, Class C, Class D and Class E, while only
A, B, and C are commonly used.
• Each class allows for a range of valid IP addresses,
shown in the following table.
Class Address Range Supports
Class A 1.0.0.1 to 126.255.255.254 Supports 16 million hosts on each of 127
networks.
Class B 128.1.0.1 to 191.255.255.254 Supports 65,000 hosts on each of 16,000
networks.
Class C 192.0.1.1 to 223.255.254.254 Supports 254 hosts on each of 2 million
networks.
Class D 224.0.0.0 to 239.255.255.255 Reserved for multicast groups.
Class E 240.0.0.0 to 254.255.255.254 Reserved for future use, or Research and
Development Purposes.

118. IP address breakdown
• Every IP address is broken down into four sets
of octets and translated into binary to represent the
actual IP address.
• The below table is an example of the IP
255.255.255.255.
IP: 255 255 255 255
Binary
value:
11111111 11111111 11111111 11111111
Octet value: 8 8 8 8

119. • For an example, let's break down the IP
"166.70.10.23" in the following table.
IP: 166 70 10 23
Binary value: 10100110 01000110 00001010 00010111
Numerical
value:
128+32+4+2=
166
64+4+2=70 8+2=10 16+4+2+1=23
Network prefix and host number:
The network prefix identifies a network and the host number identifies a
specific host

120. Dotted Decimal Notation
• IP addresses are written in a so-called dotted
decimal notation
• Each byte is identified by a decimal number in
the range [0..255]: