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DEEPAK.P
COMMUNICATION NETWORKS
Mr. DEEPAK P.Associate ProfessorECE Department
SNGCE
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DEEPAK.P
UNIT 3Inter Networking
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Inter network
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Inter networkInternetworking is the practice of connecting a computer
network with other networks through the use of gateways.
Internetworking is a combination of the words inter ("between") and networking;
The most common example of internetworking is the Internet
Inter networking can be classified in to two1. Connection oriented or concatenated of virtual circuit
subnets2. Connectionless or Datagram
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Connection Oriented Virtual circuit
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Virtual Circuit• A virtual network link is a link that does not consist of a
physical (wired or wireless) connection between two computing devices but is implemented using methods of network virtualization.
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Concatenated of Virtual Circuit
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B
A X.25
Subnet 1
Subnet 3
Host
ATM
M M
Subnet 2
SNA
Multi protocol router (Gateway)
Routers
SNA-System Network Architecture
Virtual Circuit Establishment1. Subnet shows that the destination is remote destination and
builds a virtual circuit to the router nearest to the destination.
2. It then constructs a virtual circuit from that router to an external gateway (multi protocol router).
3. This gateway notes down the existence of this virtual circuit in its table and builds another virtual circuit to a router which is in the next subnet.
4. This process continues until the destination host has been reached.
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Virtual Circuit Establishment
5. After building the virtual circuit, data packets begin to flow along the path
AdvantageBuffer can be reserved in advanceShorter header can be usedSequencing can be guaranteed
DrawbacksThere is no alternate path to avoid congestionRouter failure creates big problems
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Connection less
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Datagram Internetworking
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Path 2 B
A
Subnet 1
Subnet 3
Host
M M
Subnet 2Multi protocol router (Gateway)
Routers
MM
Path 1
Datagram packets
Datagram packets
Datagram InternetworkingThe packets that are forwarded across the Internet are known
as IP datagramsAn IP datagram consists of a header and a payloadThe header contains information that allows Internet routers to
forward the datagram from the source host to the destination host
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Datagram InternetworkingHeader contains all information needed to deliver datagrams
to destination computer 1. Destination address2. Source address3. Identifier4. Other delivery information
Router examines header of each datagram and forwards datagram along path to destination
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Advantage& Disadvantage DatagramAdvantage
Higher BandwidthDeal with congestion in a better wayIt is robust in Router failure
DrawbacksNo guarantee of packetsAddressing is difficultLonger header is needed
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Datagram forwarding in IP
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Delivery of an IP datagramInternetwork is a collection of LANs or point-to-point links
or switched networks that are connected by routers.
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IP forwarding Using DatagramThe IP forwarding algorithm, commonly known as IP
routing.It is a specific implementation of routing for IP networks and
gives a more directed approach in forwarding datagram's over a network.
In order to achieve a successful transfer of data the algorithm uses a routing table to select a next-hop router as the next destination for a datagram.
The IP address that is selected is known as the next-hop address.
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Datagram forwarding in IPAn IP network is a logical entity with a network numberWe represent an IP network as a “cloud”
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Networks and IP addressingIP address:
Network part + Host part
Network:Any host can physically be reached by any other host
without intervening routerAll hosts in the same network have the same network
number
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Forwarding DatagramsHeader contains all information needed
to deliver datagrams to destination computerDestination address– Source address– Identifier– Other delivery information
Router examines header of each datagram and forwards datagram along path to destination
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Routing tablesEach router and each host keeps a routing table which tells the
router how to process an outgoing packet
Main columns:
1. Destination address: where is the IP datagram going to?2. Next hop: how to send the IP datagram?3. Interface: what is the output port?
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IP Frame format
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Beginning of Data
Header
Payload
IP HeaderProtocol Version(4 bits) : This is the first
field in the protocol header.
This field occupies 4 bits.
This signifies the current IP protocol version being used.
Most common version of IP protocol being used is version 4 while version 6 is out in market and fast gaining popularity.
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IP HeaderHeader Length(4 bits) : This field provides
the length of the IP header.
The length of the header is represented in 32 bit words.
Since this field is of 4 bits so the maximum header length allowed is 60 bytes.
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IP HeaderType of service(8 bits) :
The first three bits of this field are known as priority bits and are ignored as of today.
The next 4 bits represent type of service and the last bit is left unused.
The 4 bits that represent TOS are : minimize delay, maximize throughput, maximize reliability and minimize monetary cost.
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IP HeaderTotal length(16 bits): This represents the
total IP datagram length in bytes.
Since the header length (described above) gives the length of header and this field gives total length so the length of data and its starting point can easily be calculated using these two fields.
Since this is a 16 bit field and it represents length of IP datagram so the maximum size of IP datagram can be 65535 bytes.
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IP HeaderIdentification(16 bits): This field is used for uniquely identifying the IP
datagrams.
This value is incremented every-time an IP datagram is sent from source to the destination.
This field comes in handy while reassembly of fragmented IP data grams.
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IP HeaderFlags(3 bits): This field comprises of three bits.
While the first bit is kept reserved as of now, the next two bits have their own importance.
The second bit represents the ‘Don’t Fragment’ bit.
The third bit represents the ‘More Fragment’ bit.
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IP HeaderFragment offset(13 bits):
In case of fragmented IP data grams, this field contains the offset( in terms of 8 bytes units) from the start of IP datagram.
So again, this field is used in reassembly of fragmented IP datagrams.
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IP HeaderTime to live(8 bits) : This value represents number of hops that the
IP datagram will go through before being discarded.
The value of this field in the beginning is set to be around 32 or 64 (lets say) but at every hop over the network this field is decremented by one.
When this field becomes zero, the data gram is discarded. So, we see that this field literally means the effective lifetime for a datagram on network.30 DEEPAK.P
IP HeaderProtocol(8 bits) :
This field represents the transport layer protocol that handed over data to IP layer.
This field comes in handy when the data is demultiplex-ed at the destination as in that case IP would need to know which protocol to hand over the data to.
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IP HeaderHeader Checksum(16 bits) : This fields
represents a value that is calculated using an algorithm covering all the fields in header (assuming this very field to be zero).
This value is calculated and stored in header when IP data gram is sent from source to destination and at the destination side this checksum is again calculated and verified against the checksum present in header.
If the value is same then the datagram was not corrupted else its assumed that data gram was received corrupted. So this field is used to check the integrity of an IP datagram.32 DEEPAK.P
IP HeaderSource and destination IP(32 bits each) : These fields store the source and destination
address respectively.
Since size of these fields is 32 bits each so an IP address os maximum length of 32 bits can be used.
So we see that this limits the number of IP addresses that can be used.
To counter this problem, IP V6 has been introduced which increases this capacity.
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IP HeaderOptions(Variable length) : This field
represents a list of options that are active for a particular IP datagram.
This is an optional field that could be or could not be present.
If any option is present in the header then the first byte is represented as follows :
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IP Header
In the description above, the ‘copy flag’ means that copy this option to all the fragments in case this IP datagram gets fragmented.
The ‘option class’ represents the following values : 0 -> control, 1-> reserved, 2 -> debugging and measurement, and 3 -> reserved. Some of the options are given below :
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IP Header
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IP HeaderData: This field contains the data from the
protocol layer that has handed over the data to IP layer. Generally this data field contains the header and data of the transport layer protocols. Please note that each TCP/IP layer protocol attaches its own header at the beginning of the data it receives from other layers in case of source host and in case of destination host each protocol strips its own header and sends the rest of the data to the next layer.
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Routing tablesNext hop and interface column can often
be summarized as one columnRouting tables are set so that datagrams gets
closer to the its destination.
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Delivery with routing tables
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Tunneling
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TunnelingIt is used when source and destination networks of same
type are to be connected through a network of different type.
Consider an ethernet network to be connected to another ethetnet through a WAN
The task is send on IP packet from host A of Ethernet 1 to the host B of ehernet 2 wia a WAN.
In this example, the IP packet do not have to deal with WAN.
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TunnelingThe host A&B do not have to deal with WAN
The multiprotocol routers M1 and M2 will have to understand about IP and WAN packet.
Therefore WAN can be imagined to be equivalent to a big tunnel extending between multiprotocol routers M1 and M2.
So this technique is called Tunneling
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Tunneling
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WAN Tunnel
B
Ethernet 2
M2
IP
Ethenet Frame
IP
WAN packet
IP packet is inside the payload field of WAN packet
Header
A
Ethernet 1
M1
HOST HOST
Sequence of events in Tunneling
1. Host A construct a packet containing the IP address of host B
2. It then inserts this IP packet in to ethernet frame.
3. This frame is addressed to the multi protocol router M1.
4. Host A then puts this frames on Ethernet.
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Sequence of events in Tunneling
5. When M1 receives this frames, it removes IP packet, inserts it in the IP payload packet of the WAN network layer packet and addresses the WAN packet to M2.
6. The multi protocol router M2 remeoves the IP packet and send it to host B in an ethernet frame.
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ARP
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ARPAddress Resolution Protocol (ARP) is a
telecommunications protocol used for resolution of network layer addresses into link layer addresses
ARP was defined by RFC (radio Frequency Committee) 826 in 1982
If a machine talks to another machine in the same network, it requires its physical or MAC address.
ARP is used to convert an IP address to a physical address such as an Ethernet address
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ARPIP address of the destination node is broadcast and the
destination node informs the source of its MAC address.
Assume broadcast nature of LAN
Broadcast IP address of the destination
Destination replies it with its MAC address.
Source maintains a cache of IP and MAC address bindings
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ARP
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ARP
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NetworkLayer
Link Layer
IP
ARP NetworkAccess RARP
Media
ICMP IGMP
TransportLayer
TCP UDP
ARP
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Send broadcast request
receive unicast response
ARPA host wishing to obtain a physical address broadcasts an
ARP request onto the TCP/IP network.
The host on the network that has the IP address in the request then replies with its physical hardware address.
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ARPProblem: Router A needs to forward an IP datagram to
router B (which is on the same Ethernet LAN)
Router A knows the IP address of B.
But the IP datagram must be encapsulated within an Ethernet frame, whose Ethernet destination address is the address of B’s NIC
How can A discover the Ethernet Address of B’s NIC?
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ARP
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ARPA uses the Address Resolution Protocol (ARP) to discover
B’s NIC Ethernet address.
A broadcasts an Ethernet frame on the LAN.
The payload of the frame is an ARP request: who has address 148.4.20.10 (B’s IP address).
All computers in the LAN hear the broadcast.
The computer whose IP address is 148.4.20.10 (B) replies to A: my ethernet address is aa:bb:cc:dd:ee:ff.
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ARPNow A has the ethernet address of B ’s NIC, and can send
the IP datagram to B encapsulated within an Ethernet frame with destination address aa:bb:cc:dd:ee:ff.
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ARP request/reply Ethernet Frame
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ARP Header format
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ARP HeaderHardware type (HTYPE)
This field specifies the network protocol type. Example: Ethernet is 1.
Protocol type (PTYPE) This field specifies the internetwork protocol for which the
ARP request is intended. For IPv4, this has the value 0x0800. The permitted PTYPE
values share a numbering space with those for Eather typeHardware length (HLEN) Length (in octets) of a hardware
address. Ethernet addresses size is 6.
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ARP HeaderProtocol length (PLEN) Length (in octets) of addresses used in the upper layer
protocol. (The upper layer protocol specified in PTYPE.) IPv4 address size is 4.
Operation Specifies the operation that the sender is performing: 1 for request, 2 for reply.
Sender hardware address (SHA) media address of the sender.
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ARP HeaderSender protocol address (SPA) internetwork address of the
sender.
Target hardware address (THA) media address of the intended receiver. This field is ignored in requests.
Target protocol address (TPA) internetwork address of the intended receiver. ARP protocol parameter values have been standardized
and are maintained by the Internet Assigned Numbers Authority (IANA).
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ICMP
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ICMPData delivery using IP datagram is the best delivery
scheme but it has two deficiencies.
Lack of error control
Lack of assistance mechanism.
These ICMP can compensate these deficiencies.
It is a companion to IP protocol
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ICMP
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IGMP
IP
ICMP
ARP
RARP
Network Layer
ICMPInternet Control Message Protocol
It is a network layer protocol
Used mostly for error reporting at the IP level.
But its message is not passed directly to the data link layer
The messages are first encapsulated inside IP datagram before going to the lower layer
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Encapsulation of ICMP messages
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ICMP
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ERROR REPORTING
ICMP MESSAGE
QUERY
ICMPThe error reporting message reports problems occurred at
router or a host.
The query message , which occurs in pairs , help a host or a network manager to get specific information from a router or another host
ICMP does not correct errors , it simply reports them.
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ICMP error reporting
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Destination un reachable
Error reporting
Re directionSource Quench
Time exceeded
Parameter problems
Source quench--- Flow control to IP
Parameter problem– Any ambiguity in the header part
Re direction--- Host routing table updation is caaried out
ICMPFor example, if the TTL of the IP datagram reaches 0
when it reaches a router, the datagram is dropped by the router, and the router sends an ICMP message back to the source of the datagram to inform it that the datagram was dropped because its TTL reached 0 (Time Exceeded)
If a router does not know how to route an IP datagram, it drops the datagram an send an ICMP message back to the source (Destination unreachable).
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ICMP Messages with message number
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ICMP header
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ICMP headerType field defines the type of message
Code field specifies reason for particular message
Checksum for error reporting
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DHCP
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DHCPDynamic Host Configuration ProtocolAllows a computer to obtain an IP address and
other parameters from a DHCP server
A DHCP server is a program running in some fixed computer in the LAN that has been configured to assign IP addresses from a given range to other computers in the LAN that request them
The DHCP server also provides things like default routes, and DNS server addresses
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DHCPDHCP requests are broadcasted within the local
LAN (frame dest ff:ff:ff:ff:ff:ff)If the DHCP server is in a different LAN, the
request won’t reach that server.
One way around this is to configure some other computer in the LAN as a dhcp relay agent : the relay will intercept the DHCP request and forward it to the DHCP server on the other LAN
Simplifies management, as only one DHCP sever needs to be configured for the entire network, rather than having to configure separate DHCP servers for each LAN76 DEEPAK.P
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Subnetting
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Subnet
A sub network, or subnet, is a logically visible subdivision of an IP network.
The practice of dividing a network into two or more networks is called subnetting.
All computers that belong to a subnet are addressed with a common, identical, most-significant bit-group in their IP address
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Subnet
Subnetting an IP Network can be done for a variety of reasons, including organization, use of different physical media (such as Ethernet, FDDI, WAN, etc.), preservation of address space, and security.
The most common reason is to control network traffic.
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IP Packet
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IP Packet
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IP Packet
An IP packet has two fundamental components:
1. IP header IP header contains many fields that are used by routers to
forward the packet from network to network to a final destination.
Contains layer 3 info Fields within the IP header identify the sender, receiver,
and transport protocol and define many other Parameters.
2. Payload Represents the information (data) to be delivered to the
receiver by the sender. Contains data & upper-layer info
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IP Versions
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IPV4
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IPV4
Internet Protocol is one of the major protocol in TCP/IP protocols suite.
This protocol works at Network layer of OSI model and at Internet layer of TCP/IP model.
Thus this protocol has the responsibility of identification of hosts based upon their logical addresses and to route data between/among them over the underlying network.
IPv4 is a connectionless protocol for use on packet-switched networks.
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IPV4
Internet Protocol version 4 (IPv4) is the fourth version in the development of the Internet Protocol (IP) Internet, and routes most traffic on the Internet.
However, a successor protocol, IPv6, has been defined and is in various stages of production deployment.
IPv4 is described in IETF publication RFC 791
It operates on a best effort delivery model, in that it does not guarantee delivery, nor does it assure proper sequencing or avoidance of duplicate delivery.86 DEEPAK.P
IPV4
IPv4 uses 32-bit (four-byte) addresses, which limits the address space to 4294967296 (232) addresses.
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IPv4 - Packet Structure
The encapsulated data is referred to as IP Payload.
IP header contains all the necessary information to deliver the packet at the other end.
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IPv4 - Packet Structure
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IPv4 - Addressing
IPv4 supports three different type of addressing modes:
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 client sends data to the targeted server
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IPv4 – Unicast Addressing
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IPv4 – Broadcast Addressing Mode:In this mode the packet is addressed to all
hosts in a network segment.
The Destination Address field contains 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 client sends packet, which is entertained by all the Servers:
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IPv4 – Broadcast Addressing Mode:
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IPv4 – Multicast Addressing Mode:
This mode is a mix of previous two modes, i.e. the packet sent is neither destined to a single host nor all the host on the segment.
In this packet, the Destination Address contains special address which starts with 224.x.x.x and can be entertained by more than one host.
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IPv4 – Multicast Addressing Mode:
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IPV6
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IPV6
Internet Protocol version 6 (IPv6) is the latest revision of the Internet Protocol (IP), the communications protocol that provides an identification and location system for computers on networks and routes traffic across the Internet.
IPv6 was developed by the Internet Engineering Task Force (IETF) to deal with the long-anticipated problem of IPv4 address exhaustion.
IPv6 is an Internet Layer protocol for packet-switched internetworking and provides end-to-end datagram transmission across multiple IP networks,
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IPV6
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IPV6 & IP V 4
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IPV6 & IP V 4
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Routing
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RoutingRouting means finding a suitable path for a
packet from sender to destination
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RoutingRouting is the main function of the network
layer.
Network layer protocols responsible for deciding which output line an incoming packet should be transmitted on.
Routing is usually performed by a dedicated device called a router.
The path with lowest cost is considered as best.
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RoutingThe routing algorithm is the part of a network
layer software responsible for deciding which output line a packet should be transmitted on
Each router stores information about forwarding in a routing table
– Initialized at system initialization– Must be updated as network topology changesA routing table contains a list of destination
networks and next hop for each destinationNote that a router has several IP addresses!– One IP address per interface
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Classification of RoutingRouting schemes differ in their delivery semantics:Unicast: delivers a message to a single specific node.
Broadcast: delivers a message to all nodes in the network.
Multicast: delivers a message to a group of nodes that have expressed interest in receiving the message.
Anycast: delivers a message to any one out of a group of nodes, typically the one nearest to the source.
Geocast: delivers a message to a geographic area.
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Classification of RoutingRouting can be classified in to two
Static Routing or Non adaptiveDo not consider measurement and estimate of current
traffic and topology on their routing decisionsEg. Flooding, Flow based routing, Shortest path
Dynamic Routing or AdaptiveChange routing decisions to reflect changes in topologyEg. Distance vector routing , Link state routing
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Routing Protocols
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Routing Protocols
RIP(Routing information Protocol
Interior (Routing inside an autonomous System)
Exterior (Routing between autonomous system)
OSPF(Open shortest path first
BGP (Border gateway Protocol)
Desirable Properties of Routing Algorithms
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Static Routing
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FloodingIt is a static algorithm
Every incoming packet is sent out on every outgoing line except the one it arrived on.
It will generate vast no of duplicate packets.
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Flooding
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Application of FloodingMilitary application
Distributed database application
Wireless network
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Selective Flooding
Variation of flooding is selective flooding
Do not send every incoming packet out on every line.
It sends to the line that are going approximately in the right direction.
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Flow-based RoutingSimilar in spirit to minimum distance,
but takes traffic flow into consideration.
From the known average amount of traffic and the average length of a packet you can compute the mean packet delays using queuing theory.
Flow-based routing then seeks to find a routing table to minimize the average packet delay through the subnet.
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Flow-based RoutingAssume that traffic is huge from A to B
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H
D
C
FE
G
B
A
TAKE THE ROUTE AGEFC INSTEAD OF ABC
Shortest pathLinks between routers have a cost associated
with them.In general it could be a function of
DistanceBandwidthAverage trafficCommunication costMean queue lengthMeasured delayRouter processing speed
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Shortest path algorithmsThe shortest path algorithm just finds the
least expensive path through the network, based on the cost function.
Dijkstras algorithms
Bellman-ford algorithms
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Dynamic Routing
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Distance vector Routing
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Distance Vector RoutingIn this routing each router 'telling the
neighbors about the whole network'.
Each router maintains a table called vector.Each router periodically shares its knowledge about the
entire network with its neighbors.
The working principle of distance vector routing includes
Knowledge about the whole networkRouting only to neighbors Information sharing at regular intervals
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Distance Vector Routing
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Distance Vector RoutingIn distance vector algorithms, each router has to
follow the following steps:It counts the weight of the links directly
connected to it and saves the information to its table.
In a particular period of time, the router sends its table to its neighbor routers (not to all routers) and receives the routing table of each of its neighbors.
Based on the information the router receives from its neighbors' routing tables, it updates its own.
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Distance Vector RoutingDistance vector routing is also called
Distributed bellman- ford algorithmFord-Fulkerson algorithm
In distance vector routing Cost is based on
Hop countTime delayNo of packets in a queue.
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Distance Vector Routing
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Distance Vector RoutingThe cost of each link is set to 1. Thus, the least cost path is simply the path
with the fewer hops.The table below represents each node’s
knowledge about the distance to all other nodes:
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Distance Vector RoutingInitially, each node sets a cost of 1 to its
directly connected neighbors and infinity to all the other nodes.
Below is shown the initial routing table at node A:
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Distance Vector RoutingDuring the next step, every node sends a
message to its directly connected neighbors. That message contains the node's personal list of distances.
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Distance vector Routing
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12
25
40
14
23
18A17
0
21
9
29
24
36
18
27
7
20
3120
24
0
11
33
22
31
19
8
30
19
60
20
14
7
9
22
28
36
24
22
40
3119
21
22
10
9
0
A
I
H
I
I
HH
A
I
-
K
K
20
28
20
17
30
1812
8
10
0
15
6
A I H K J
New Routing Table for JJA delay is 8 JI delay is 10
JH delay is 12
JK delay is 6
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Distance Vector RoutingProblem (assume that cost is 1 for each link)
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Link state Routing
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Link state RoutingLink state algorithms are sometimes
characterized informally as each router 'telling the other router about its neighbors'.
The concept has 5 parts
Discover it’s neighbors and learn their network addressMeasure the delay or cost to each of it’s neighbors.Construct a packet telling all it has learned.Send this packet to all other routers.Compute the shortest path to every other router.
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Link state Routing
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neighbor to all routers
neighbor to all routers
neighbor to all routers
neighbor to all routers
neighbor to all routers
neighbor to all routers
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Routing for Mobile Hosts
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Routing for mobile HostsWireless hosts are often mobile, changing location
over time
This mobility of a wireless host may cause the host to connect to Different networks at different points of time.
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CIDR
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CIDR
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CIDR
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